Abstract: In view of the insufficiencies of the work made by earlier workers in characteristic solution,description of particle motion and derivation of size of separation through computational mathematic modeling,it is first proposed in the paper to obtain solution of particle motion equations through computer programming using Matlab software. It is demonstrated that: all the particles can theoretically reach the balanced state,but some of the particles may not be able to do so within their effective residence time in hydrocyclone; and the majority of the particles can move in a radical direction to the narrow annular zone before they are finally separated. In this case they are in a quasi-equilibrium state. The research work made is an improvement and development of the existing equilibrium orbit theory and plays a positive role in realizing the highest level in separating efficiency and sharpness.