In order to investigate the cavitation characteristics of centrifugal pumps under low flow rates, the cavitating flows in the centrifugal pump typed IS50—65—160 with three different bladenumber impellers were numerically simulated based on the k—ε turbulent model combined with Rayleigh—Plesset cavitation model by using the software ANSYS CFX 14.5. Meanwhile, grid independence check was carried out to verify the accuracy of calculation. The effect of blade numbers on the cavitation characteristics in the pump was firstly analyzed from the points of suction performances, torque as well as axial forces acted on impellers. The results showed that as the blade number increased from 4 to 8, the pump head increased while the variable regulation of its efficiency was quite complicated. Both the head-drop and torque-drop curves of impellers with three different blade numbers had the same shape of creeping dropping, with the corresponding break-down points occurring asynchronously. The axial forces acted on impellers almost kept constant as the amount of head dropping was 3% or higher. The vapor volume in one blade was larger than others, and finally a significantly asymmetric distribution occurred on all blades. It was firstly obtained that the creeping-drop characteristics of both pump head and torque acted on the impellers were possibly related to onset of asymmetric blade cavitation phenomenon. Moreover, this study to some extent can also provide some reference for the design of centrifugal pump in the industry in case of avoiding serious cavitation occuring at low flow rates.