Based on the requirements of human comfort in buildings and the concision of physical model, CFD software called Airpak 2.1 was used to simulate indoor air temperature field and air velocity field in a room. In this paper, two types of indoor air supply are compared; i.e. lateral air supply system and ceiling air supply system. The numerical results of air velocity field, Predicted Mean Vote (PMV) and Predicted Percent Dissatisfied (PPD) are analyzed in detail. It is shown that the ceiling air supply performs better than lateral air supply under specified boundary conditions.