A model is implemented to simulate the Directional Brightness Temperature（DBT） of three dimensional urban targets based on the computer graphics and the environment simulation algorithm.Using urban three dimensional scene

the model is able to calculate the surface cells seen by the sensor in a given Field of View（FOV） and the sunlit and shade patterns created by three dimensional urban surface structures.The DBT over urban areas is accurately simulated in the Instantaneous Field of View（IFOV）.Model validation is conducted by comparing the simulated DBT with observed DBT

which demonstrates that the model has a high accuracy with the（Root Mean Square Error） RMSE of 0.7 K.The model can be used to describe the thermal anisotropy of urban targets at the micro-scale.The simulated results of DBT for scale model of urban targets reveal significant DBT variations for complex urban surfaces.The hot spot effect appears obviously in the upper hemispheric plot of DBT.