There is a dynamic relationship between outdoor air temperature and solar radiation. Based on the meteorological data of 13 typical cities in south China and by the regression analysis method, the dynamic fitting function between the solar radiation and the land surface temperature and the function of temperature difference between the air and land surface changing over time are established. And the correlation coefficient R 2 are over 0.97 which indicates that the results can significantly reflect the variation of data points，then the dynamic relationship between outdoor air temperature and solar radiation is obtained. The results suggest that solar radiation is a linear function of the outdoor air temperature and time in the plateau, while logarithmic function of both in the plains. The study will provide convenient method for building cooling load calculation, and provide scientific basis for studying the dynamic relationship between the solar radiation and the building cooling load as well as the suitability of the solar energy air conditioning.