Abstract: To ensure construction safety and ventilation efficiency during open-type tunnel boring machine (TBM) construction in deep-buried water conveyance tunnels crossing high-gas coal-measure strata, a water conveyance tunnel in Xinjiang was taken as the engineering background. The FLUENT numerical simulation method was used to compare and analyze the effects of “centralized air supply through a single outlet” and “air supply through dual outlets formed by diversion from a single main air duct via a tee joint” on the tunnel flow field and gas distribution. The results show that, under a constant total air supply capacity, the dual-outlet arrangement forms upper and lower dual jets near the tunnel face and weakens the local strong recirculation at the bottom. The coefficient of variation of wind velocity near the tunnel face decreases from 0.69 to 0.16, and the cross-sectional wind velocity distribution within the range of 0–150 m becomes more uniform. In terms of gas migration, the gas concentration near the tunnel face under the dual-outlet arrangement can be reduced to below 0.0015, compared with about 0.0026 under the single-outlet condition. At 10 m from the tunnel face, the gas concentration reduction under the dual-outlet condition is about 40%, which is higher than the 25% reduction under the single-outlet condition.