In order to improve undesirable flow phenomena like spinning and partial flow in forebays of deep tunnel inflow pumping stations, the flow in forebays was numerically simulated based on the RNG k-ε turbulence model, and rectification measures applicable to this kind of urban drainage pumping station were investigated. Numerical simulation results revealed the presence of several adverse hydraulic phenomena within the forebay and inlet pool of the pump station, including local vertical spinning, spiral flow, oblique flow, and uneven velocity distribution with higher velocity at the top and lower velocity at the bottom, resulting in poor hydraulic conditions in the inlet channel of the pump station. A rectification measure combining a double-layer ring plate and two groups of guide piers can suppress the vertical spinning, spiral flow and oblique flow in the forebay and inlet pool. This rectification measure significantly improves the inlet conditions of the flow channel, leading to more uniform flow velocity distribution at the inlet of the inflow channel.Consequently, the pump inflow water conditions become better, and the operation reliability of the pumping station is improved.