The control of pH value is an important part of water and fertilizer integrated nutrient solution circulation control system. In the process of water and fertilizer control, pH value in the optimal control is conducive to the development of root system and absorption of most minerals. In the process of nutrient solution regulation, due to the slow diffusion of the circulating line and acid fluid, the pH adjustment process has a large time lag, and the traditional PID is difficult to achieve good results. According to the characteristics of the controlled object, a mathematical model describing the process was established, and a pH control system with secondary mixed fertilizer was designed. Combining with the characteristics of parameter normal setting, the fuzzy PID does not need accurate mathematical model and the Smith predictor can perform the pure lag compensation, the parameter self-tuning fuzzy PID control was introduced into Smith prediction, which can overcome the influence of lag time on control system and improve the accuracy of the model. In order to verify the algorithm and the effectiveness and superiority of the system, the PID and Fuzzy-Smith control algorithm were simulated respectively, and the performance tests under different irrigation quantities were carried out. The experimental results show that the average maximum overshoot of pH value under Fuzzy-Smith control of different irrigation amounts is 0.83%. The average rise time of nutrient solution from pH value 8.0 to 6.0 is 157 s. It is better than the conventional PID control result which is 2.55% and 189 s. The Fuzzy-Smith control algorithm proposed in this paper has good control stability and dynamic performance, and can meet the requirements of automatic control of pH value of nutrient solution.