The visualization of flow is one of the fundamental methods to investigate the dispersion characteristics of heat and air pollutants in urban areas. This research made a major attempt to visualize the thermally distributed flow by introducing the Schlieren system in the thermal stratification wind tunnel for the first time. First, Owen's estimate equation concerning refractive index of the air was used to investigate relative influence of pressure to temperature. As a result, it was 0.004[K/(m/s)] or less under wind-speed not exceeding 2m/s. Next, floor heated wind tunnel experiments were carried out, and the Schlieren images observed numbers of waving thermal mass bulging from the heated floor toward obliquely backward. Also, when the windward is stable, development of thermal stratification at the leeward by heated floor was restrained due to the influence of the inversion layer by the cold air from the windward. Finally, as a result of investigating the influence of building arrangement by 2D building models with heated floor, the top of cavity (L/H=1.7) was covered by the dense colored thick layer in the Schlieren images, which indicates steep temperature distribution, on the other hand, the Schlieren images was uniform inside the cavity due to the circulation flow.