In order to realize the receiving and sending of multi byte long data packets between DSP and external devices, a receiving method based on interrupt mode and a sending method based on query mode are proposed. With DSP2812 chip as the platform, the data packet length is 48 bytes, for example, to communicate with the upper computer. Once the DSP receive interrupt occurs, the receive state machine can be started to receive data packets adaptively. The sending process uses the query form to send the data in a timed or triggered manner to realize the sending of long data packets. The test results show that the method is stable and reliable, and is very suitable for miniaturization and low-cost applications, which can provide reference and help for practical engineering development.