Abstract: In view of the instability of product quality in traditional water-coal powder mixer system,a set of water-coal powder mixer system based on double-PI control was designed.The system’s working principle,hardware components and program design were introduced.The system takes OMRON C200HE PLC as core and uses analog unit AD003,DA003 and external elements to constitute adjustment circuits of quantities of coal powder and water,which realizes follower control of water-coal powder mixer system by two PID commanders.