Abstract: In order to improve the efficiency of low specific speed centrifugal pumps, the outlet angle of impeller blades is generally increased, but this will cause hump of the H-Q curve, resulting in unstable operation of the pump in the small flow area. The single-stage single suction centrifugal pump with specific speed of 47 produced by a domestic pump factory is taken as the research object, the orthogonal test method is adopted to select five factors, namely, the impeller outlet oblique cutting ratio, the outlet angle, the impeller axis oblique angle, the blade wrap angle and the blade inlet edge position. Each factor adopts four levels, and this results in a total of 16 impeller design schemes. Each scheme was carried out numerical simulation to obtain the external characteristic curve of it. The influence of five factors on the shape of the characteristic curve and the head, efficiency and shaft power of the pump under rated working conditions was studied by range analysis method. The primary and secondary order of factors affecting the stability of the characteristic curve was found to be the blade inlet edge position, the impeller outlet edge chamfer, the impeller axis inclination angle, the outlet angle and the blade wrap angle. Based on the analysis results, the optimal combination scheme of the impeller was obtained, and the scheme was numerically simulated and tested. The results show that the H-Q curve of the optimized scheme is stable and the pump efficiency is increased by 1.4%. The reason for improving the stability is observed from the impeller rotation field before and after optimization, i.e. secondary flow area is generated at the outlet of the impeller rear cover plate to obtain higher lift. The relative velocity gradient at the impeller outlet decreases, and the "Jet wake" phenomenon weakened or even disappears with loss significantly .