Based on the analysis of fluid flow at the inlet of the impeller, one kind of hydraulic design method for inlet guide vane was proposed, used to adjust the operation point of centrifugal pump. The goal of the method lies in reducing the incidence loss and recirculation loss and improving the hydraulic performance for centrifugal pump at off-design condition. Based on the SIMPLEC algorithm, the Reynolds averaged Navier-Stokes equation and RNG k-ε turbulent model equation were solved. Then, the 3-D turbulent flow field of the centrifugal pump with inlet guide vane was simulated with the condition of various angles. Numerical results of operation performance are agreed well with the experimental date. Furthermore, the basic principle and mechanism of inlet guide vane pre-whirl regulation were analyzed.