Digital Signal Process (DSP) is a MCU which could process control signal, and was often used in the implementation of control systems. With the improvement of user's requirements and the development of electronic technology, the application programs needed to be upgraded. Taking TMS320DSPF28335 as an example, this paper described a DSP program upgrade method that was separated from the JTAG port and implemented by serial port, which avoided exposing the equipment and transmission errors with long JTAG cable. Different from the common upgrade method, this method proposed in this paper could execute the application program when DSP was powered on. This satisfied the situation where the application program needed always executed when the device powered on, and also avoided the trouble of the users used the jump command to execute the application program. And the host computer software was designed to verify the effectiveness of this method.