In view of the uncertainties such as time-varying state, nonlinearity and hysteresis of the double-tank water liquid level system, a design scheme based on sliding mode control is proposed, which solves the defects in the accuracy and efficiency in terms of traditional PID control method. Through the analysis of the water double-tank, two models of transfer function and state space equation are established successively, and the corresponding sliding mode surface and approaching rate are designed so as to realize the variable structure nonlinear control of Double-tank water level. The simulation results show that the designed controller in this paper greatly reduces the overshoot and adjustment time of the system by the simulation results. And the superiority of the proposed scheme is verified. Finally, it includes that the variable structure controller with sliding mode has good adaptability and strong anti-interference ability.