Abstract: Rice damage is very serious during harvesting, at the same time the design of the threshing unit mainly depends on experience in our country. And threshing proceeding of rice is a research focus. From impact view, the function of the distance and maximum pressure distribution were made during the collision process between the rice and the threshing component. As parameters such as rectangular protractor, elastic modulus, Poisson's ratio, ultimate strength of spike-tooth and rice, et al, were given, the critical relatively velocity between the rice and the spike-tooth was calculated. The experiments results showed that it were according with the theory analysis. It provided a theoretical foundation for threshing designing in the future.