Abstract: A simplified single particle dynamic model is proposed to study the particle trajectory in the classifier rotor.The particle movement in the radial direction is assumed resulting from local equilibrium of two forces, the air drag force and the centrifugal force. By this equilibrium, the fine and coarse particles to be separated have different trajectories in the classification zone. For the convenience of finding the solution, the original governing equation is converted to one in rotating coordinate system. Particle trajectories are determined according to different rotor rotating speeds, different gas flow rates, different blade spaces, and different blade angles. Numerical results show that the increase of the rotating speed and the decrease of the gas flow rate can significantly reduce the cut size. Narrow blade space causes more collision between particles and the wall. With respect to decreasing the cut size of the classifier,the blade with negative angle is better than that of zero angle, and zero angle is better than positive angle, while other parameters of the vortex classifier are kept the same.