The purpose of this study is to investigate the effect of boundary conditions on the temperature distribution and thermal comfort of a radiant floor heating system and their practical application to commercial buildings. Indoor thermal environment, along with human response, was studied by means of CFD. The three-dimensional temperature distribution was numerically simulated with the zero-equation turbulent model. And two typical operating models, which there is and there is no windows in the room were analyzed in detail. The results show that the radiant floor heating system can meet the demand of comfortable degree, and that the temperature field is enormously influenced by boundary conditions. It is necessary to install curtains to decrease the radiant heat transfer of the cooling glass surface and other control methods to ensure the room to be a thermal comfortable environment.