The correction and interpolation were conducted on the radiation observation in Mojiaquanwan and Yushu around Xining, and the spatial distribution and inter-annual variation of solar radiation were analyzed systematically. The results stows that the global radiation is relatively high over the Qinghai Plateau and the distribution shows a tendency of higher in the West is and lower in the East; the global radiation value was higher in the 1970's and obvious low in the 1980's, increased again from the end of the 1980's to the beginning of 1990's, but decreased after the middle 1990's. The high and low periods in the 1970s and 1980s are closely related to the cloud amount and precipitation over Qinghai Province and volcanic eruptions across the world during the same periods. Volcanic eruption was an important cause of the decrease in solar radiation.