The performance of multi-stage Electrical Submersible Pumps (ESPs) under different flow conditions and its life span with sand production are commonly predicted by the Computational Fluid Dynamics (CFD) simulations. The mesh generation methodology and optimum grid number are usually validated by pump water catalog curves. Then, the validated mesh geometry is adopted in high viscosity, multiphase flow, and sand erosion simulations to study the effects including but not limited to: discrete phase bubble diameter, turbulence model, body forces, and erosion models. However, the mesh validation by pump water curves is not enough in complex flow conditions, especially in the erosion simulations. Different from the pump hydraulic performance simulation, the accuracy of the erosion simulation can be affected by mesh boundary and inner layer grid thickness, especially for small particles. In addition, the mesh-type (hexahedral and tetrahedral) and size of the inner domain can also significantly affect the particle trajectory. A comprehensive mesh independent study is conducted for water, oil, and gas-liquid conditions of a mixed type ESP in this paper. Then the near-wall inflation layer thickness and inner domain grid size effect to ESP erosion simulation are well analyzed. The mesh generation methodology can be applied to other turbomachinery simulations to improve accuracy.