Aimed at some complex CFD models which may generate very poor grid by using unstructured grid, and is bound to increase the difficulty of calculating, numerical simulation of a low specific-speed centrifugal pump was carried out between the unstructured grid and structured grid at the different operating points in CFX software. The results of simulation show that the pressure distributions of structured grid model is closer to the design value and separated vortex is more obvious near short blade surface region. Compared the simulation results with the experimental values, it is found that the result of structured grid can meet the design requirement. That confirms the numerical simulation computation is feasible with accuracy.