Abstract: In order to investigate the performance prediction of high rotating speed axial-flow pumps, a QY90-4.4-1.5 submersible axial flow pump with specific speed 550 were used in the study, and its particular impeller and guide vane were designed on the basis of arc method and streamline method. The performance of the pump was numerically predicated by CFD. Firstly, three-dimensional physical modeling and unmapped grid division were made by Pro/E and ICEM software, and then the internal flow fields were numerically calculated with standard k-ε turbulence model, meanwhile the performances of the pump model were also diagnosed by comprehensive analysis. The results presented that the calculated data was in good accordance with the experimental data. Because of the simulation of backflow and secondary flow has not been developed completely, there was a certain error for pump Q-H, Q-P, Q-η curves when it deviates from the rated condition largely. By analyzing the pressure and relative velocity distribution of the blade surface on the optimal condition, the results showed that larger drop pressure gradient in the leading edge was developed because of the impact flow leaves, and wide low-pressure zone on the back of blade led to cavitation. Meanwhile, the speed was increased with the radius direction and no radial-branch velocity was developed. Overall, the results basically was according with the assumption of uniform distribution for velocity circulation with the radius in impeller.