In order to investigate the variation of global solar radiation (Rs) and its cause in Hainan Island, long-term daily global solar radiation and routinely meteorological data such as daily sunshine hours, maximum and minimum temperatures at Haikou and Sanya stations were used. Climate tendency rate and Mann-Kendall test were used to analyze the annual, rainy season and dry season variations of daily Rs. Multiple linear regression was implemented to analyze the meteorological factors that influencing the variations of daily Rs. The results indicated that the climate tendency rate was 0.021、0.004、0.038 MJ/m2 for daily Rs of full year, rainy season and dry season at Haikou during 1961-2013, respectively. While the climate tendency rate was -0.68, -0.658, -0.714 MJ/m2 for daily Rs of full year, rainy season and dry season at Sanya during 1993-2013, respectively. The variation of daily Rs presented a fluctuation trend. The “dimming” appeared in 1975-1992, 1975-1990 for Rs of full year and rainy season at Haikou, respectively. Whereas the daily Rs for dry season decreased first and then increased, the “dimming” was in 1967-2003, and the “brightness” was after 2003. And the significant “dimming” was 1995 and 1988-1989.. The daily Rs for full year, rainy season and dry season at Sanya has presented a decline trend since 1993. The obvious “dimming” was in 1999-2013, 2000-2003 and 2009-2011, 1996-2001 and 2004-2013, respectively. The jump year were 1997, 1995 and 1995, respectively. In general, the Rs resources of Sanya were more abundant than that of Haikou. Sunshine duration was the mainly cause of daily Rs variations at Haikou and the Rs for full year, rainy season of Sanya. However, the daily average temperature was the main reason for daily Rs variation of dry season at Sanya.