The Coandă effect on jet flow can be solved effectively using the jet fan with a pitch angle in highway tunnels. In this study, the ventilation efficiency of the jet fan with a pitch angle in the range 0–12° is tested using the computational fluid dynamics (CFD) method with experimental validation. The mean air age in volume (MAA-V) is applied to evaluate the ventilation effectiveness in the full space and clearance space of tunnel. The results show that the jet fan with a pitch angle can significantly alleviate vortices caused by the jet flow. The pitch angle of 7° can provide a desirable compromise for MAA-V, found to be 13.62% and 20.67% younger than that of 0° for the full and clearance spaces, respectively. Furthermore, the pressure-rise coefficient at different pitch angles is also investigated, and the maximum is obtained at the pitch angle of 7° as well. Finally, the pitch angle of 7° is determined as the optimal angle for the jet fan, which is of great benefit for improving ventilation effectiveness and saving installed power in highway tunnels.