After introducing the design method of digital current (DC) power supply and the circuit schematic diagram and software flow chart of the key part, the paper designs the core processor based on ARM 32-bit Cortex™-M3 as controller, which, in hardware, has the features of high accuracy and simple circuit, and in function, parameters can be set both through keystroke and computer serial port. Meanwhile, the voltage and current of power supply are of high accuracy, quick in adjust response and with small output voltage ripple.