Simulation study on random motion and mixing characteristic of soybean in a horizontal rotary drum was carried out based on discrete element method with EDEM. The effect of the rotation speed and load of the drum on particle random motion and mixing index was analyzed. It was found that the increasing of the rotation speed improved the random motion of particle, enhanced the mixing effect of particles, and speeded up the mixing process. Soybean load had the opposite effect. With the increasing of load, although the particle random motion was increased in the radial direction of the drum, the phenomenon of accumulation was more obvious and the random motion was significantly lower along the rotary drum axis direction. The mixing rate of particles was slow and the mixing effect became poor. 