The 3D models of impeller and volute were produced by professional software Pro/E, the gap between impeller and volute was appended to impeller. The impeller inlet and volute outlet were extended properly to reduce the effect of boundary conditions on inner flow. The meshes required for the calculations were generated and checked by using the CFD pre-processing package, GAMBIT. Due to the geometry of the pump is very complex, unstructured tetrahedral mesh is used. “EquiAngle Skew” and “EquiSize Skew” of the grid were all less than 0.95, so the grid quality is good. Relativity examination of grid number was done for each model with different blade number. When the effect of grid number on pump characteristics is less than 1%, it could be ignored. The grid numbers of volute and impellers with different blade number are 480 000 respectively. Fig. 1 shows the 3D model and wall grid of the calculation region with 5 blades.