To accurately obtain the contact parameters between the discrete element model of potassium fertilizer particles and improve the efficiency of the simulation test, the contact parameters between potassium fertilizer particles were calibrated and the potassium fertilizer particle model was optimized. Firstly, the nonstandard ball model of potassium fertilizer particles was established in EDEM 2020 software. Secondly, taking the contact parameters between the discrete element model of potassium fertilizer as the experimental factors and the accumulation angle as the response value, the central composite test was designed to obtain the contact parameters of the discrete element model of potassium fertilizer particles. Finally, based on the response surface method of the regression model, the particle size of the potassium fertilizer particle model and the smoothness of the filled particle model were optimized to obtain the optimal discrete element particle model of potassium fertilizer, and the verification tests before and after optimization were carried out. The experimental results show that the relative error between the optimized simulation test and the physical bench test is 0.58%, and the simulation time after optimization is saved by 67.16% compared with that before optimization. The optimized potash particle model improves the simulation efficiency on the premise of ensuring the accuracy of simulation, and the research results can be used as a reference for studying the characteristics of potash particle material by the discrete element method.