Abstract: Abstract: In order to ensure the safe and stable operation of pump station when the suction sump is under the ultra-low water level (the ultra-low water level is higher than the pump installation elevation yet lower than the designed low level of the suction sump), the Tianshan first-grade pump station is taken as study object in this paper. Site research shows that when the pump station runs under the ultra-low water level in long time, the noise and vibration of the pump unit are increased, the impeller and blade are severely caved and the normal operation of pump station is affected. In order to solve these adverse effects, the combined rectification scheme is proposed, which consists of diversion platform, underwater vortex suppression plate and W type diversion pier near the back wall. The flow pattern, the velocity distribution and the axial velocity uniformity of bell-mouth inlet under the original scheme and rectified scheme were analyzed through numerical simulation and experimental research respectively. The numerical simulation results showed that violent vortexes appeared on side wall, bottom and surface of the suction sump due to the ultra-low water level and large velocity gradient in suction sump. These vortexes deteriorated the flow pattern in suction sump, and this situation was exacerbated by excessive hanging height and the distance between back wall and water inlet. But a vortex at the bottom and 2 surface vortexes of the suction sump were completely removed, and the side wall vortex of the suction sump was controlled; the area of backflow and stagnant water shrank dramatically after the combined rectifier scheme was adopted. In addition, the uniformity of axial velocity distribution of bell-mouth inlet was increased from 62.3% to 87.5%, 25.2% higher than before, which greatly improved the water flow pattern in suction sump. In the combined rectifier scheme, the diversion platform eliminated the whirlpool at the bottom of the suction sump, and improved the flow pattern between the bell-mouth and the bottom of the suction sump. The underwater vortex suppression plate effectively suppressed the intake swirl at the surface of the suction sump and weakened the vortex on the side wall. The W type diversion pier near the back wall made the back wall W type, which gave better hydraulic characteristics to the back wall and weakened the backflow and stagnant water near the back wall. It was also observed in the model test and PIV (particle image velocimetry) test that some adverse phenomena such as sixth types intake swirl on the suction sump surface and other serious vortexes on the side wall and bottom of the suction sump disappeared and the velocity distribution of specific area of the suction sump was more reasonable than the suction sump before rectification. In summary, the combined rectification scheme proposed in this paper can provide good water inlet condition for water pump unit under ultra-low water level of suction sump, and provide technical transformation basis for pumping station running under other low water level.