Abstract: Based on the consideration of the dispersed phase interaction with continuous phase, applying the Reynolds stress model and the stochastic trajectory model to the continuous and dispersed phase, the particle motion trajectory is simulated successfully, which can visually show the separation process in a hydrocyclone. According to the analysis of the particle motion trajectory, the effect factors of the separation perform- ance, such as particle diameter and particle injection region ,as well as particle flow characteristic within circulation stream are known. Besides，using the ratios of the particles quantities in underflow and overflow, the grade efficiency curve can be plotted. The results of the simulation calculation are verified by a comparison of the experimental data with simulation values. Based on these results another plotting method of the grade efficiency curve for engineering handle is provided.

Key words: Hydrocyclone, Numerical simulation, Solid particle Stochastic trajectory