Objective: The rotational speed of the roller of the rice mill was optimized to reduce the crushing rate of rice grains in the process of whitening. Methods: The extrusion filling model was established by using SolidWorks software, and the collision contact model of single rice grain and two rice grains was established by using the particle bond model in EDEM software. The collision process of rice grains with different moisture content at different falling speeds was simulated, and the collision results of corresponding rice grains were observed. Results: There were three critical states of rice grains in the process of collision, which were intact rice grains, slightly broken rice grains and broken rice grains. Under the set moisture content range, the crushing rate of rice grains increased with the increase of moisture content and collision velocity, and the critical crushing rates of intact rice grains in the collision model of single grain and two grains were similar, which were 23.5 m/s and 22.0 m/s, respectively. Conclusion: The speed and moisture content have a significant effect on the crushing morphology of rice grains, and when the moisture content is 10.6%, the maximum speed of non-crushing of rice grains is 22.0 m/s, at this time, the crushing rate of rice grains is small and meets the demand of milling.