Fish-friendly designs were done on a traditional pump which was effective for reducing fish mortality during passage through the pumping station. However, optimization designs which were good for fishfriendliness had disadvantageous effect on pump cavitation performance. With the aim of improving the cavitation performance of fish-friendly axial-flow pump, a commercial computational fluid dynamic software ANSYS CFX, which showed a fair agreement with the experimental results, was used to predict the cavitation performance. The predicted NPSHr,3% of original pump was increased from about 3.5m to 9m after fish-friendly designs were done, which was unacceptable for pump running. Therefore, the inner flow field characteristics were numerically analyzed and the result indicated that there was vortex generated next to the hub and the inlet angle of attack was unsuitable, which was the primary reason for cavitation inception. The vortex formation mechanism was discussed and the airfoil section near the hub was redesigned to restrain the vortex generation. Furthermore, the design parameters of other airfoil sections were corrected to make streamlines smooth and fit the profile of blades. The optimization and numerical simulation results showed that the flow field was stable and flow transition around the head of airfoil section was smooth without velocity increment. The streamlines near the blade suction side fit the surface and there was no vortex generated. By reducing the inlet pressure, the predicted NPSHr,3% value of optimized fishfriendly axialflow pump was reduced to about 3m, which was absolutely enough for pump running. The research result provided a complete design method for fish-friendliness and optimization of hydrodynamic performance for axial-flow pump.