To enhance the efficiency of carbon monoxide (CO) emission control during drill-and-blast construction in high-altitude tunnels and to improve the working environment for personnel, a tunnel currently under construction at a high altitude was investigated. Utilizing the computational fluid dynamics simulation software Fluent, three factors were examined under forced ventilation conditions: the distance between the air duct and the tunnel face, the position of the air duct, and the varying elevations. To model the diffusion characteristics of harmful CO gases. The simulation results indicate that when the air duct is positioned too close to the tunnel face, vortices form, causing CO accumulation near the tunnel face, which is detrimental to the effective dispersal of CO from this area. Conversely, when the duct is positioned too far, the airflow loses a significant amount of kinetic energy before reaching the tunnel face, which also hinders the effective removal of harmful CO gases in the vicinity of the tunnel face. Optimal removal efficiency of harmful CO gases near the tunnel face is achieved when the air duct is placed at a distance of 25.2 m from the tunnel face and located at the top of the tunnel. This configuration significantly improves the working environment for personnel within a short period. Compared to plain regions, the distance between the duct and the tunnel face in high-altitude areas should be approximately 3 \sqrt{S} (S is the cross-sectional area of the tunnel) that of the plain regions. The trend of CO movement within the tunnel is generally consistent across different altitudes. As the altitude increases, the concentration of CO also increases, and the speed of CO movement within the tunnel decreases, necessitating longer ventilation times in high-altitude areas.