In order to understand the design of cooling water circulation system, a design study of cooling water circulation system of vacuum moisture regain machine is put forward. The phenomenon of "water shortage" often occurs in the cooling water circulating tank of vacuum dehumidifier, which makes the cooling water entering the condenser insufficient, which causes the efficiency of vacuum dehumidifier to decrease and affects the product quality. In this paper, an automatic water supply device is designed by using automation technology and condensate recovery technology. At the same time, the condensate from the production line is recovered as the water supply source. When the cooling circulating water tank is "short of water", the water supply device automatically supplies water. The results show that after the automatic water replenishment device is installed in the cooling water circulation system of vacuum humidifier, the normal operation of the equipment can be guaranteed, the permeability rate is greatly improved, the stability of the system is improved, and the precise control of cooling water replenishment is realized.