Inspired by the mixing entropy of the particle system, a measuring device based on the plane array CCD camera was built in order to carry out a series of measurements for the particle system composed of spherical particles with mean particle sizes of 2.6 mm and 1.25 mm respectively. The average speed and the angle of slope on the surface of the particle system were calculated through the pyramid-layered optical flow algorithm and the image method. The following conclusions are drawn. The subtle changes in the particle separation process can be described by the total entropy of the particle system. The average velocity of the flow layer on the surface of the particle system is affected by the angle of slope, and those two show a direct proportional relationship. Within the rotation speed range where the movement state of mixed particles is continuous avalanche, the global entropy of particle system, the average velocity of surface flow layer and the angle of slope have similar trend, indicating that the separation degree of particle system can be judged by the aid of the average speed and the angle of slope.