With the rapid urbanization in China, the study of the cooling effect of urban heat island is of great significance to promote the sustainable development of urban ecological environment. In this paper, the influence of block morphology and roof materials on radiant heat and surface temperature are analyzed by using an offline urban canopy model. The results show that the height and the width of the building and the width of the street have great influences on the surface temperature of the urban canopy. When the street width is increased by 3 m, the ground temperature would rise about 3.5 K. However, if the street width increases, the radiation cutoff effect caused by the multiple reflections would be weakened. Thereby, the wall will release more energy, which can lower its temperature by 1.5 K. The canopy temperature increases first, and then decreases by about 0.4 K after sunrise. The change in roof materials also has great impacts on radiation, heat flux and surface temperature. Compared with the gray cement roof, the cooling roof with high-albedo white paint can reduce the net radiation by about 380 W m^-2 and the roof surface temperature would reduce by about 10 K. The block morphology and the roof material have a direct impact on the urban radiant heat environment.