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Global solar radiation (Rs) is an important elementary datum for crop modeling and reference evapotranspiration (ETo) estimation, but only 1/20 of Chinese weather stations can observe it directly. It is a common method for estimating Rs to use empirical model based on temperature data, which are easy to get. Based on the temperatures of 20 weather stations in south of China from 1982 to 2014, parameters of six different forms of Bristow—Campbell (B—C) and Hargreaves (Harg) methods were calibrated, and the applicability of abovementioned methods and fifteen support vector machine (SVM) parameter input forms were evaluated. The results showed that SVM model was better than B—C method and Harg method as a whole. The SVM model with maximum temperature (Tmax), minimum temperature (Tmin), relative humidity (RH) and precipitation (P) as input variables had the highest precision. On average, R2 and RMSE from the twenty weather stations were 0.80 and 3.20MJ/(m2·d), respectively, even when it included precipitation data, Rs was not negative and even greater than the extraterrestrial total radiation (Ra). R2 from the twenty weather stations was 0.74 on average, and RMSE was 3.72MJ/(m2·d) when based on temperature data. Different input variables had different influences on the SVM model forecasted Rs, the input variables of Tmax and Tmin were superior to ΔT. In addition to temperature data, when the model had the relative humidity and rainfall data, it was showed that RH+P > RH > P. Among the empirical models, the B—C model’s M1 and M3, and the Harg models’ M10 and M12 were preferable, their R2 were 0.69~0.70, RMSE was about 4.0MJ/(m2·d). While the M10 and M12 had higher request to the meteorological data, which needed the data of dayly temperature and precipitation. There existed the dayly Rs overestimation or negative problems when it rained.