Abstract: Abstract: Automatic poppet valve is a key component of reciprocating pump, which directly influences its performance and lifespan by controlling flow direction of fluid. Many researchers focus mainly on constant stiffness coefficient springs, due to its widespread application in the automatic poppet valve. Previous research already proves that spring plays an important role in the dynamic properties of poppet valve. The main function of spring is to balance inertia force. Studies also suggest that impact velocity and lag height gradually decreases with the increases of stiffness coefficient and preload. However, the increases of stiffness and preload makes head loss rise. Therefore, only by adjusting different combinations of spring stiffness and preload, it is difficult to reduce impact velocity and lag height while reducing head loss. This contradiction restricts the further improvement of reciprocating pump performance. In addition, the determination of the preload and stiffness of spring is often based on empirical formulas in the design process about constant stiffness coefficient spring. To solve these problems, application of variable stiffness coefficient spring on the pump valve was proposed in this paper. In the meantime, a new optimization design method for it was established. The main research contents of this paper included: (i) A mathematical model on the motion properties of valve disc was established under the condition which spring stiffness coefficient was variable. In this model, dynamics differential equation of valve disc motion, continuous flow equation of fluid between valve gaps and initial condition were all considered about. Based on above mathematical model, a computer simulation program was compiled to solve this simulation model by using of Runge-Kutta method. (ii) In order to verify accuracy of simulation model, two contrast tests were carried out. Firstly, lift of valve disc was compared between simulation results and measured results when stroke frequency was 74 min-1. In the process of measurement, the lift of valve disc was measured by lift sensor and pressure in the liquid cylinder was measured by semiconductor pressure transducers. The contrast result showed that the error was less than ±8％. Secondly, by changing parameter of stroke frequency, maximum lift was compared under different stroke frequencies, the error was less than ±10％. In summary, the above comparison showed that simulation model met the requirement of precision. (iii) According to above simulation model, we selected many different combinations of stiffness and preload for the constant stiffness coefficient spring for simulation comparison. After calculation, there was a mutual contradiction between impact velocity, lag height and head loss. In other words, impact velocity and lag height would increase with head loss reduced. Subsequently, in response to above deficiencies, three common types of spring: stiffness decreasing type, stiffness increasing type and stiffness constant type were chosen in the simulation. By comparing with curves of lift, velocity and head loss, it was demonstrated that stiffness decreasing type can improve the suction performance of reciprocating pump, while impact velocity and lag height were not significantly increased. (iv) Based on the numerical simulation model of valve disc motion properties, optimization simulation model of variable stiffness spring parameters was established. In this optimization model, the objective function was that maximum head loss was minimum. The constraint condition was that impact velocity satisfied the theory of no impact. Genetic algorithm and pattern search were used to solve this optimization model. In the end, compared with the constant stiffness coefficient spring, the maximum head loss for variable stiffness spring was reduced by 20.85%. In conclusion, variable stiffness coefficient spring can be used for improving suction performance of reciprocating pump and alleviating the occurrence of cavitation. Besides, this optimization method has a certain guiding significance for guiding design process of spring parameters on the pump valve.