Abstract: This paper describes the characters of a control system EPICS, which is popular in large accelerator laboratories in the world. It is a software toolkit for building process control system for a wide variety of experimental and industrial applications. Its software tools provide independent and expandable modules for system configuration, distributed process control, run-time database, alarm manager, etc. This paper describes the process of creating device support module for the magnet power supply device with serial port and the skeleton of the control system. It also describes the characters of ASYN software. And this work prepares for building the control system of the 30 MeV linac. The EPICS toolkit will be applied in the control system of the linac in FEL research, with satisfactory