In order to reveal the internal flow laws of large-scale mixed-flow pumps, a high specific speed mixed-flow pump was simulated based on the standard k—εturbulence model and SIMPLEC algorithm by using software FLUENT. The axial velocity and circulation distributions of steady flow under working conditions of 0.8Qopt, 1.0Qopt, and 1.2Qopt at impeller outlet were obtained. The numerical results showed that the flow was stable under all the three working conditions; the axial velocity gradually decreased from hub to tip; the circulation flow pattern of the mixed-flow was nonlinear at impeller inlet, and approximately uniform at impeller outlet. The negative pressure zone which gradually expanded with the flow rate increasing existed obviously at the suction side. The study provided a certain reference for the hydraulic design of mixed-flow pump.