diff --git a/av1/av1.cmake b/av1/av1.cmake
index 3eb4a1f..f538b2b 100644
--- a/av1/av1.cmake
+++ b/av1/av1.cmake
@@ -170,6 +170,8 @@
             "${AOM_ROOT}/av1/encoder/ethread.h"
             "${AOM_ROOT}/av1/encoder/extend.c"
             "${AOM_ROOT}/av1/encoder/extend.h"
+            "${AOM_ROOT}/av1/encoder/external_partition.c"
+            "${AOM_ROOT}/av1/encoder/external_partition.h"
             "${AOM_ROOT}/av1/encoder/firstpass.c"
             "${AOM_ROOT}/av1/encoder/firstpass.h"
             "${AOM_ROOT}/av1/encoder/global_motion.c"
diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index 4c7c8da..edf22c0 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -26,6 +26,7 @@
 #include "av1/encoder/bitstream.h"
 #include "av1/encoder/encoder.h"
 #include "av1/encoder/ethread.h"
+#include "av1/encoder/external_partition.h"
 #include "av1/encoder/firstpass.h"
 #include "av1/arg_defs.h"
 
@@ -2204,8 +2205,17 @@
   return update_extra_cfg(ctx, &extra_cfg);
 }
 
-// TODO(chengchen): implement this function
-static aom_codec_err_t ctrl_set_external_partition() { return AOM_CODEC_OK; }
+static aom_codec_err_t ctrl_set_external_partition(aom_codec_alg_priv_t *ctx,
+                                                   va_list args) {
+  AV1_COMP *const cpi = ctx->ppi->cpi;
+  aom_ext_part_funcs_t funcs = *CAST(AV1E_SET_EXTERNAL_PARTITION, args);
+  aom_ext_part_config_t config;
+  // TODO(chengchen): verify the sb_size has been set at this point.
+  config.superblock_size = cpi->common.seq_params->sb_size;
+  const aom_codec_err_t status =
+      av1_ext_part_create(funcs, config, &cpi->ext_part_controller);
+  return status;
+}
 
 #if !CONFIG_REALTIME_ONLY
 static aom_codec_err_t create_stats_buffer(FIRSTPASS_STATS **frame_stats_buffer,
diff --git a/av1/encoder/encoder.h b/av1/encoder/encoder.h
index b915cf3..336602f 100644
--- a/av1/encoder/encoder.h
+++ b/av1/encoder/encoder.h
@@ -35,6 +35,7 @@
 #include "av1/encoder/block.h"
 #include "av1/encoder/context_tree.h"
 #include "av1/encoder/encodemb.h"
+#include "av1/encoder/external_partition.h"
 #include "av1/encoder/firstpass.h"
 #include "av1/encoder/global_motion.h"
 #include "av1/encoder/level.h"
@@ -2800,6 +2801,12 @@
    * Available bitstream buffer size in bytes
    */
   size_t available_bs_size;
+
+  /*!
+   * The controller of the external partition model.
+   * It is used to do partition type selection based on external models.
+   */
+  ExtPartController ext_part_controller;
 } AV1_COMP;
 
 /*!
diff --git a/av1/encoder/external_partition.c b/av1/encoder/external_partition.c
new file mode 100644
index 0000000..b8bde66
--- /dev/null
+++ b/av1/encoder/external_partition.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2021, Alliance for Open Media. All rights reserved
+ *
+ * This source code is subject to the terms of the BSD 2 Clause License and
+ * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+ * was not distributed with this source code in the LICENSE file, you can
+ * obtain it at www.aomedia.org/license/software. If the Alliance for Open
+ * Media Patent License 1.0 was not distributed with this source code in the
+ * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+ */
+
+#include "av1/common/common.h"
+#include "av1/encoder/external_partition.h"
+
+aom_codec_err_t av1_ext_part_create(aom_ext_part_funcs_t funcs,
+                                    aom_ext_part_config_t config,
+                                    ExtPartController *ext_part_controller) {
+  if (ext_part_controller == NULL) {
+    return AOM_CODEC_INVALID_PARAM;
+  }
+  ext_part_controller->funcs = funcs;
+  ext_part_controller->config = config;
+  const aom_ext_part_status_t status = ext_part_controller->funcs.create_model(
+      ext_part_controller->funcs.priv, &ext_part_controller->config,
+      &ext_part_controller->model);
+  if (status != AOM_EXT_PART_OK) {
+    return AOM_CODEC_ERROR;
+  }
+  ext_part_controller->ready = 1;
+  return AOM_CODEC_OK;
+}
+
+aom_codec_err_t av1_ext_part_init(ExtPartController *ext_part_controller) {
+  if (ext_part_controller == NULL) {
+    return AOM_CODEC_INVALID_PARAM;
+  }
+  av1_zero(ext_part_controller);
+  return AOM_CODEC_OK;
+}
+
+aom_codec_err_t av1_ext_part_delete(ExtPartController *ext_part_controller) {
+  if (ext_part_controller == NULL) {
+    return AOM_CODEC_INVALID_PARAM;
+  }
+  if (ext_part_controller->ready) {
+    const aom_ext_part_status_t status =
+        ext_part_controller->funcs.delete_model(&ext_part_controller->model);
+    if (status != AOM_EXT_PART_OK) {
+      return AOM_CODEC_ERROR;
+    }
+  }
+  return av1_ext_part_init(ext_part_controller);
+}
+
+bool av1_ext_part_get_partition_decision(ExtPartController *ext_part_controller,
+                                         aom_partition_decision_t *decision) {
+  assert(ext_part_controller != NULL);
+  assert(ext_part_controller->ready);
+  assert(decision != NULL);
+  const aom_ext_part_status_t status =
+      ext_part_controller->funcs.get_partition_decision(
+          &ext_part_controller->model, decision);
+  if (status != AOM_EXT_PART_OK) return false;
+  return true;
+}
+
+bool av1_ext_part_send_partition_stats(ExtPartController *ext_part_controller,
+                                       const aom_partition_stats_t *stats) {
+  assert(ext_part_controller != NULL);
+  assert(ext_part_controller->ready);
+  assert(stats != NULL);
+  const aom_ext_part_status_t status =
+      ext_part_controller->funcs.send_partition_stats(
+          &ext_part_controller->model, stats);
+  if (status != AOM_EXT_PART_OK) return false;
+  return true;
+}
+
+bool av1_ext_part_send_features(ExtPartController *ext_part_controller,
+                                const aom_partition_features_t *features) {
+  assert(ext_part_controller != NULL);
+  assert(ext_part_controller->ready);
+  assert(features != NULL);
+  const aom_ext_part_status_t status = ext_part_controller->funcs.send_features(
+      &ext_part_controller->model, features);
+  if (status != AOM_EXT_PART_OK) return false;
+  return true;
+}
diff --git a/av1/encoder/external_partition.h b/av1/encoder/external_partition.h
new file mode 100644
index 0000000..b6c8d7b
--- /dev/null
+++ b/av1/encoder/external_partition.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2021, Alliance for Open Media. All rights reserved
+ *
+ * This source code is subject to the terms of the BSD 2 Clause License and
+ * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+ * was not distributed with this source code in the LICENSE file, you can
+ * obtain it at www.aomedia.org/license/software. If the Alliance for Open
+ * Media Patent License 1.0 was not distributed with this source code in the
+ * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+ */
+
+#ifndef AOM_AV1_ENCODER_EXTERNAL_PARTITION_H_
+#define AOM_AV1_ENCODER_EXTERNAL_PARTITION_H_
+
+#include <stdbool.h>
+
+#include "aom/aom_codec.h"
+#include "aom/aom_external_partition.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*!\cond */
+
+typedef struct ExtPartController {
+  int ready;
+  aom_ext_part_config_t config;
+  aom_ext_part_model_t model;
+  aom_ext_part_funcs_t funcs;
+} ExtPartController;
+
+aom_codec_err_t av1_ext_part_create(aom_ext_part_funcs_t funcs,
+                                    aom_ext_part_config_t config,
+                                    ExtPartController *ext_part_controller);
+
+aom_codec_err_t av1_ext_part_init(ExtPartController *ext_part_controller);
+
+aom_codec_err_t av1_ext_part_delete(ExtPartController *ext_part_controller);
+
+bool av1_ext_part_get_partition_decision(ExtPartController *ext_part_controller,
+                                         aom_partition_decision_t *decision);
+
+bool av1_ext_part_send_partition_stats(ExtPartController *ext_part_controller,
+                                       const aom_partition_stats_t *stats);
+
+bool av1_ext_part_send_features(ExtPartController *ext_part_controller,
+                                const aom_partition_features_t *features);
+
+/*!\endcond */
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // AOM_AV1_ENCODER_EXTERNAL_PARTITION_H_