The Large Eddy Simulation is an sppropriate method to simulate a lot of kinds of turbulence. In this paper, the authors apply this method to the simulation of an indoor air flow, which has the temperature variation and the natural ventilation through the openings. The turbulence should be simulated by a 3-dimensional analysis, however, it takes much longer time than 2-dimensional one. Therefore, 2-dimensional analysis is tested for the simulation of turbulence. These numerical simulations are compared with the similar model test to examine the results. The boundary condition for temperature, which is adopted here, expresses the heat transmission through the wall. The results of the numerical simulations are expressed as the distribution of temperature and stream line. These results show the good agreement with the model test. The Large Eddy Simulation is thought to be able to simulate this type of air flow. The results of a 2-dimensional analysis, which uses a larger Smagorinsky constant than a 3-dimensional case by 70 %, agree well with those of a 3-dimensional one. The boundary condition for temperature is thought to be suitable in these numerical analyses.