The city main structure was simplified to the street structure in which both sides are buildings and the middle is road. The street structure was assumed straight forward and infinite within a pixel, the contribution of pixel radiance from the top of the buildings, the vertical walls and the road was computed respectively using geometrical optics method. Then the bidirectional reflectance function(BRF) of the main structure of the city was constructed in large scale. In the micro-scale, the BRF of the structure surface itself was considered too. For an urban pixel, there may be vegetation, so the BRF of vegetation was considered in the model and the BRF over urban areas was constructed. The BRF of an urban pixel was calculated and the sensitivity was analyzed, the characteristic of BRF over urban areas is the emergence of specular reflection peak and hot spot, and the height of building and vegetation coverage have significantly effects on the BRF of an urban pixel.