The calculation of the solar radiation heat is important to the accuracy of heating load prediction, especially in area with sufficient solar radiation, e.g. western Sichuan in China. However, only a few researches are focused on the specific effects of solar radiation heat in this area. Therefore, based on a practical residential building in Western Sichuan and the survey data, the heating load during the day and night in a heating season under different working conditions are compared in this paper. The influence of solar radiation on the heating load of residential buildings in Western Sichuan is analyzed, and the correctness of the simulation software is verified by experiments. The results show that the solar radiation will greatly increase room base temperature in the daytime. In a heating season, the heating load of the building increases by 26.12% without considering solar radiation heat. During the day (9:00 to 18:00) and night (18:00 to 9:00), the heating load increases by 35.69% and 19.80%, respectively. Besides, solar radiation mainly affects the south exterior wall in a north-south residential building. The heating load of south rooms is 27.52% less than north rooms, with 35.92% less during the day and only 22.08% less during the night.