Abstract: When the axial flow pump is in reverse power generation, different operating conditions and geometric overcurrent forms may lead to certain hydraulic instability. Taking the bi-directional axial flow pump unit of a pumping station as the research object, the SST k-ω turbulence model is applied, the full flow channel numerical simulation, and analysis of forward and reverse power generation are carried out. The results show that under the rated speed of axial flow pump device, the overall efficiency of reverse power generation is higher than that of forward power generation; under the optimal conditions, the reverse power generation has a reasonable pressure distribution in the pump section, and the flow line is relatively smooth. The outlet pressure pulsation stability of the forward generating conductive vane is poor. By comparing the vortex evolution of guide vane segment with the force change law of impeller, the large-scale vortex inside guide blade of forward power generation is the reason for irregular pressure pulsation at the outlet of the guide blade and lower efficiency under optimal working conditions, and the higher water head of the impeller section of the reverse power generation causes it to be subjected to more axial force. The unsteady flow in the guide vane of forward power generation is the essential reason for the greater radial force of the impeller. The results can provide theoretical support and engineering reference for the operation stability of bi-directional axial flow pump unit and axial flow pump unit with front (rear) guide vane under the power generation condition.