The direct solar radiation intercepted by each surface inside the sunlight greenhouse was computed. The result shows that the diurnal course of direct solar radiation intercepted by east and west wall was different from that of the others. For shorter sunlight greenhouse, if neglecting effect of east and west wall , it will decrease the heat gain in greenhouse on the east and west wall. At the same time, it will neglect the shade areas produced by the east and west wall, and overrate the solar radiation on the other surfaces inside the greenhouse. With the length of greenhouse decreasing, the overrated value will increase. It will lead to error when the thermal environment of greenhouse was analyzed. The heat flux of each surface was measured. The course of heat accumulation and heat release of the east and west wall and its change with the length of greenhouse were analyzed. Therefore, for shorter sunlight greenhouse, the effects of the east and west wall on the heat gain of greenhouse must be considered. It can be referenced for the decision of the length of sunlight greenhouse and the layout of the crop.