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 tanks to achieve level stabilisation and control, which is widely used in various fields of industrial production. Liquid level control is the key to the performance of the whole control system due to the existence of hysteresis and other problems in the control. Serial control of the sub-loop has a rapid control role, it can effectively overcome the impact of the disturbance into the sub-loop, improve the dynamic characteristics of the object, so in order to achieve better control performance, this design uses serial control to achieve the level of double-capacity water tank fixed value control. Double-capacity water tank level series control system to the tank level as the controlled quantity, first of all, the characteristics of the tank, the establishment of its mathematical modelling, and then the use of MATLAB on the simulation of the tank as well as PID parameter adjustment, and finally through the response curve to analyze the control performance of the system. The simulation results show that the double-capacity water tank level series control performance is good, the system can achieve the level of static-free regulation, and anti-interference ability is strong, with good dynamic and steady state performance.