Centrifugal pump performance has transient effect obviously during rapid changing period and the pump hydrodynamic performance of transient is different from steady-state process. In order to research the speed regulation characteristics and the inner flow mechanism of the centrifugal pump, numerical method of solving the unsteady fluid flow around the accelerating blade was established. The dynamical changes of the pressure and velocity were simulated by Fluent6.2, using standard k-epsilon turbulence model, PISO algorithm. The dynamic mesh technology and UDF were used to deal with the moving boundary caused by changing speed. Simulation results shown that faster angular acceleration made larger pressure fluctuations. Different regulated time had different influence in the system transient characteristics. And the evolution of the internal flow rate present strong transient performance in the regulating process. The study confirmed the feasibility of dynamic mesh method in solving the transient fluid flow during pump regulating period.