The fracturing technology has been widely applied to break up the formation in oil & gas industry. The flow dynamics and erosion phenomenon of frac sleeve in fracturing process is important but has not been studied previously. In this paper, the dynamics is studied numerically with special reference to the effect of sand mass flow rate. The simulation is conducted using a coupled approach of Computational Fluid Dynamics and Discrete Element Method. The influence of port parameters such as shape, size and number arrangement on the erosion rate was investigated. Based on this study, motion characteristics of fracturing fluid and sand particles are obtained, the structure parameters can be optimized. The frac sleeve after structural optimization obtains better erosion resistance. This study shows that Computational Fluid Dynamics could be a useful tool to study the dynamics and internal flow of fracturing tool.