Abstract: Aiming at the tedious operation of digital signal process (DSP) program upgrading in medium and low speed Maglev train levitation diagnosis system, an online upgrading method for DSP program based on the existing diagnostic network controller area network (CAN) bus is designed. In the upgrading process of DSP program, the upgrade terminal sends the upgrading instruction and upgrading program file to the CAN bus. After instruction recognition, DSP will transfer to upgrade mode, receive the new file and download it to the flash memory for online upgrade. The experimental results show that this method can safely and effectively upgrade the program online for single or a batch of DSP.