As a typical representative of process control, double-capacity water tank level control is a common automation control system used to control the level of two water tanks to achieve level stability and control, which is widely used in various fields of industrial production. In actual production, the accuracy and control effect of liquid level control directly affects the production cost of the factory, economic benefits and even the safety factor of the equipment. Therefore, in order to ensure safety and convenient operation, it is necessary to research and develop advanced level control methods and strategies. The sub-loop of serial stage control has a fast control effect, which can effectively overcome the influence of the perturbation into the sub-loop and improve the dynamic characteristics of the object, therefore, this paper adopts the serial stage control algorithm to achieve the constant value control of the liquid level of the double-capacity water tank and compare it with the conventional PID control algorithm, and the realisation results show that the serial stage control has a good ability to inhibit the secondary perturbation, and it can effectively improve the system's rapidity and accuracy.