Abstract: For the new-type rotational flow grit chamber, the MRF model and the Discrete Phase Model were used to analyze the influence on sand removal efficiency of the internal flow field of the grit chamber, the trajectory of sand, the direction of impeller rotation and the relationship of the impeller movement and the water flow rate. The results showed that when the rotation direction of the impeller movement was different, the formation of axial circulation flow field was quite different, and the clockwise rotation was helpful to sand deposition and removal. When the paddle was stationary, the water flow rate had a certain impact on the sand settlement. When the water flow rate was small, more sand was accumulated in the grit chamber, and when the flow rate was larger, the escape rate of the sand also increased. When the water flow rate was constant, the variation of the paddle speed had some impact on the removal of sand. When the paddle speed was small, the formation of the forced vortex was not sufficient to move sand toward the center of the grit chamber. When the speed gradually increased, the formation of radial flow and strong axial flow was not conducive to the settlement and removal of sand.