Concerning the wind resistant problems for buildings and structures, wind tunnel test and numerical simulation have been conducted out of consideration of effect of thermal stratification. However, it is confirmed that the observed wind profile in the typhoons is different from the wind profile in the boundary-layer type of flows and determined by strong convective effects. In this study, we numerically generate approaching flows with the effect of thermal stratification. Under these approaching flows we conduct numerical simulation for the flows around a 3D square cylinder. It is recognized that the flow field is much changed by the effect of thermal stratification and the position of the vortex on the side and the rear of the cylinder varies with the thermal conditions. As a result, the power spectrum of wind forces and pressure characteristics are also affected.