OpenCL is an open source and free heterogeneous computing framework, which is widely used in architecture processors. HXDSP is a domestic DSP chip independently developed by the 38th Research Institute of China Electronic Technology Corporation. To solve the scheduling difficulties and insufficient hardware utilization of the HXDSP heterogeneous computing platform, this work studies the task scheduling system of OpenCL during operation. The automatic task graph extraction method during the operation of OpenCL is designed, and the classic static scheduling algorithm HEFT is improved by the combination of the hardware characteristics of HXDSP and the execution model characteristics of OpenCL. Thus, a heterogeneous dual-granularity earliest finish time (HDGEFT) scheduling algorithm is proposed, and experiments are designed on the HXDSP heterogeneous computing platform for verification. The experimental results reveal that the specially designed scheduling algorithm has great advantages in execution efficiency.