Aiming at the problem of excessive negative pressure in a dropshaft caused by the inflow water tongue, the structure optimization design for the original dropshaft model was carried out. The realizable k-ε turbulence model and VOF two-phase flow model were used to study the flow regime and air pressure distribution in the original model and the optimized one under different inflow rates. A water tongue impact model was established to determine the installation elevation of the ventilation pipe bottom in the optimized model. The influence of the ventilation pipe position relative to the intake pipe on the air pressure distribution was discussed. The results show that the falling water tongue near the intake pipe blocks the normal air flow in the well, and large air recirculation zones are formed above the water tongue. The space below the water tongue cannot be replenished in time, and the sudden increase of negative pressure near the intake pipe is obvious. The established water tongue impact model can accurately predict the impact point position at the water tongue end, and the maximum error is within 10%. The installation elevation of the ventilation pipe bottom is 2.31 m, and the top elevation is slightly higher than the upper wall of the water inlet pipe. The optimized shaft model can reduce the pressure difference in the negative pressure surge zone by at least 70%, and when the angle between the ventilation pipe and the horizontal center extension line of the inlet pipe is 30°, the optimized dropshaft model has the best effect.