The rainwater pump station has the characteristics of high investment，large flow and complex flow pattern，the unreasonable size arrangement not only affects the effective performance of the pump，but also causes the increase of the construction cost of the pump station.In this paper，the actual design project of the rainwater pump station is taken as the research object，the geometric model of the pump station is constructed，based on the computational fluid dynamics（CFD），numerical simulation is carried out for the inlet flow pattern of the original design rainwater pump station，the flow field state is analyzed，and corresponding improvement measures are proposed to optimize the poor hydraulic phenomenon in the original design pump station.By comparing and optimizing the inlet flow pattern in the pump station，the performance of the pump can be brought into full play.