Based on the hourly 2 m temperature, relative humidity, surface pressure and visibility data of 158 stations in Sichuan Province during the period 1967-2008, the monthly sunny global horizontal irradiation (GHI) was calculated and integrated by using simple model for atmospheric transmission of sunshine (SMARTS). The relationship between sunny GHI and altitude was established, which was applied to the correction of GHI interpolation during the period 1990-2019, and the correction effect was verified. The results show that the sunny GHI increases logarithmically with altitude, and the higher the altitude is, the smaller the increase of sunny GHI with altitude becomes. In terms of radiation correction, the correction range of Sichuan Basin with low altitude and flat terrain is the smallest, the high-altitude plateau in western Sichuan is in the middle, the transition zone between high and low altitudes is the largest. The results of cross validation show that the annual mean absolute error of the seven stations is reduced from 182.77 kW·h·m-2 to 145.48 kW·h·m-2, while the relative error is reduced from 13.41% to 10.24%.