Abstract: Constant-current source is the more commonly used practical devices in the electronic instruments and equipment.Besides the design should be precision, but also reduce the cost.This paper introduces a new developed numerical control constant-current source which uses STM8s single chip microcomputer as the main controller, sets the required current value through the keyboardand displays, the control digital quantity can be set freely, the output current size is fully known and the size can be arbitrarily set, and high control precision, the output current range of up to 0.1 ~ 20 mA.The system has simple structure, stable working, low cost.