This paper presents an improving method of how to calculate outdoor temperature. Considering that the relative parameters of the buildings in urban areas such as relative height, orientation, vegetation cover and solar radiation which make influences on the outdoor temperature. Combining with the reality of China, the author correct the CTTC model after a further consideration of the factors that the underlying surface and the wall brings effect on the radiation absorption of different wavelengths and the heat transfer coefficients of walls in different directions. The results showed that with the increase of the relative height of buildings, there is a downtrend in outdoor temperature of buildings; the biggest drop is 1°C. With the increase of vegetation coverage, the outdoor temperature of buildings will be reduced. In the urban areas, 35% vegetation cover is the best option.