In this paper, a building canopy model is coupled with CFD for the analysis of microclimates within urban blocks under different urban and architectural planning. This model considers radiant heat exchange in the building canopy, water evaporation of vegetations and heat released from the air conditioning systems. Using this model, thermal environment of a real urban block is analyzed. The simulation results show that heat released from the air conditioning systems is one of the most important factors affecting outdoor thermal environment. Temperature of vegetation is significantly lower than that of road surfaces. However, air temperature difference is not great between zones with vegetation and other zones at 1.5m height.