The computational simulation, which predicted the temperature of the medium-sized city respectively, has conducted in this study. The computational domain includes various artificial structures of the city such as building, ground, concrete, and grass. To consider the solar radiation precisely, the unsteady numerical calculation is performed from sun rise to specific time after mid-day which the temperature is measured at. The measured and predicted temperatures are compared and those show the validity of the computational methods used in this study. The numerical methods consist of three sub-processes to reduced the computational load and to improve the flexibility of the calculation. To analyse the effect of the artificial structures. two alternative ground conditions replacing the asphalt with ground and grass are compared. The results of the alternatives show that the surface in the city filled with grass or ground can reduce the temperature of structures in the city.