Comparative experiments of free grain movement and collision under different drum speeds were carried out by using high-speed video camera on a self-designed axial flow threshing and separating device with nails teeth. The movement discipline of free grain and the movement discipline after the collision of free grain and nail tooth under different drum speeds were obtained. The results showed that the free grains movement speed increased with the increasing of drum speed. Most of the free grains moved in a medium-speed and showed a tendency of accelerating motion after crashed by the nail teeth.