The safety operation of a pump station is directly affected by the siphon formation time of a siphon outlet pipe. In order to investigate the siphon formation time characteristics and the impact of the improvement on siphon formation time, RNG k-ε turbulence model with structured grids were used to simulate the siphon outlet pipe of a pump station. The numerical simulation results show that the duration of the hydrodynamic phase is related to the inflow flux. In the hydroponic phase, the exhausting rate is related to the velocity at the water air interface. During the siphon formation process, the generation of airbags is very unfavorable for the siphon formation and configuration of a splitter plate at the top of the hump section can effectively improve the flow rate distribution in the siphon, which can accelerate the discharge of the airbags, shorten the siphon formation time and minimize the influence on the hydraulic loss.