Air Pollution is one of the main contaminants in industrial cities like Tehran, but it depends on many factors. One of the most important factors is wind field. Wind field shows how the pollutants transfer by convective mechanism. Tehran as the most polluted city of Iran (or may be Middle East) locates in a mountainous situation and is surrounded from two sides by high mountains and from two sides by desert. Therefore, the topography of Greater Tehran Area is so complex and needs more attention. We have studied the air pollution in Tehran from this point of view in this paper and used MEMO software for simulation of wind field in this area. The results show good agreement with experimental observations and show stronger wind from south to north and west-south to east-north in days and then night in reverse direction. It causes that the pollutants remain at urban area and the concentrations of pollutants reach to a serious level. One of the most important factors is wind field. Wind field shows how the pollutants transfer by convective mechanism. Tehran as the most polluted city of Iran (or may be Middle East) locates in a mountainous situation and is surrounded from two sides by high mountains and from two sides by desert. in Tehran from this point of view in this paper and used MEMO software for simulation of wind field in this area. The results show good agreement with experimental observations and show stronger wind from south to north and west-south to east-north in days and It causes that the pollutants remain at urban area and the concentrations of pollutants reach to a serious level.