In order to supply cold water for engine laboratory PLC, configuration software, HMI, and inverter are adopted to construct an automatic control system in this paper. The control system is a distributed control system, which has higher dependability and maintainability. The reading and writing network instructions are utilized to solve the communication among multi-master problem. The remote monitoring software is developed with configuration software. By measuring temperature and pressure of entrance and exit pipes, refrigeration equipments and water pumps are adjusted real-time to guarantee to supply stable temperature and pressure cold water. Therefore the quality of water is improved and power is saved. Practice proves that the system designed meets user's requirement. The system has a good reliability and high degree of automation.