This study evaluated and optimized the thermal environment inside an air-conditioned train station building using the computational fluid dynamics (CFD) method. The impacts of some air-conditioning design parameters such as supply air temperature, velocity, altitude and incidence angle on indoor thermal environment were discussed. The primary air-conditioning design scheme was optimized. The numerical results showed that when cooling loads in the waiting hall and entrance hall of the train station building kept unchanged, alternations made to the cooling air supply scheme in waiting hall would have little effect on the air distribution in entrance hall. The uniformities of velocity and temperature distributions in waiting hall showed well when side supply scheme was applied. Changing supply air temperature, velocity, altitude and incidence angle had great effects on thermal environment in the train station building. For stratified air-conditioning, in order to obtain satisfactory indoor thermal environment the supply air altitude should be at mid-height of the building with zero angle of incidence from horizontal. The results also indicated that analyzing the effect of design parameters on indoor thermal environment by CFD method provided an effective way for the optimization of design scheme.