Abstract: Numerical simulation of centrifugal pump during starting period requires an empirical formula for impeller rotating speed with time. This paper starts from the torque balance equation, and updates the rotational speed of impeller automatically, according to the input of a drive torque curve by secondary development of ANSYS CFX. A threedimensional model is established, which includes a centrifugal pump and the entire circulation pipeline. The starting period of centrifugal pump is then simulated. The result is compared with experimental curves, showing that they agree well in terms of qualitative trend of performance, and the method is effective. The method provides a new way of centrifugal pump simulation during starting period.