Abstract: NPSHr is one of the most important performance of a pump, which is mainly derived from hydraulic model tests.How to accurately predict a pump's NPSHr is a great challenge to optimize design and enhance operating stability.Based on cavitating flow feature inside a centrifugal pump, bubble growth and implosion are calculated from the Rayleigh-Plesset equation which describes the dynamic behavior of spherical bubble, filled with vapor and gas, as a function of the local pressure.A numerical simulation of two-phase flow with a homogenous mixture of gas and liquid inside a centrifugal pump was employed to explore the methodology of predicting NPSHr with numerical test approach.A numerical simulation for cavitating flow inside a low specified speed centrifugal pump was conducted in whole passage.The numerical test was carried out for the centrifugal pump at different operating conditions by varying NPSHa, which is similar to hydraulic tests, NPSHr for this pump can be predicted from the head-drop curves which were computed by numerical simulation.Meanwhile, the pressure distribution on blades surfaces, districts where cavitation occurred, and vapor volume fraction inside the flow passage of a pump could be used to investigate the cavitating flows and helpful to determine NPSHr value.It showed that the predicted result agreed with the measured results by hydraulic tests and the maximum error was within 10%.