Abstract: By analyzing and contrasting climatologically calculation methods of global solar radiation domestic and abroad, an optimal calculation formula for Hainan province was determined. In accordance with the monthly global solar radiation and percentage of sunshine from 1992 to 2003 in Haikou and Sanya areas, experiential coefficients of each month in the formula were fitted using least squares methods and monthly global solar radiations in all parts of the province were calculated. The results showed that annual variation of global solar radiation took the form of single-peak, with July maximum and February minimum. However, annual variation of global solar radiation took the form of poly-peak with July and May maximum and June relatively low value. Annual global solar radiation in this province ranged from 5145.39MJ·m^-2 to 6113.24MJ·m^-2, and the south of Hainan was big and the north was small.