Abstract: A high speed camera is used to measure the motion characteristics of particles in an axial flow fan.In the experiment the measurements of the motion characteristics of the particles are carried out on three circular surfaces.The employed particles are 1mm diameter foamed plastic spheres.From photo processing some valuable conclusions are drawn as following:(1)In the impeller channel,the concentration of the particles nearby the pressure side is higher,while the suction side is lower.And there is an area where no particle exists.(2)The trajectories of the particles approach to straight lines.Some particles collide with the pressure side and rebound from it,and the rebound angle is less than the impact angle.(3)The velocities of the particles on the pressure side is lower,while those on the suction side is higher relatively.