In order to optimize parameters of threshing system of seed corn thresher with different speeds threshing parts, and to decrease mechanical damage of corn seed kernel in the course of threshing, the process of feeding and threshing origination of single seed corn ear was analyzed by using high-speed photograph method. The testing results show that damage rate of kernels subjected intense impact is large in the feeding origination of seed corn ear; with threshing, impact changes more and more feeble, and damage rate of kernels becomes smaller and smaller too. Under state of ordinal threshing, large amounts of kernel is threshed and the moving track of threshed kernel follows the tangent direction of contacting dot of straight roller and ear, while under state of out-of-order threshing, the amount of kernel is small and the moving of threshed kernel presents disordering. Furthermore, large rotating speed of spiral roller results in the larger out-of-order threshing of ear, which influences the threshing quality and threshing efficiency of seed corn ear.