Abstract: On an overcast day, it is very difficult to measure the solar radiation flux of wall and roof of the sunlight greenhouse. Therefore, it is hard to analyze the wall heat gain and predict the temperature of the sunlight greenhouse. This paper introduced the Cloud Cover Coefficient Method to calculate the solar radiation flux. And the correlation between computed and measured solar radiation flux was analyzed. The results show the method can be applied to calculate the solar radiation of each surface inside the sunlight greenhouse.