A total solar radiation model based on the support vector machine(SVM) method is studied for calculating solar radiation in Nanjing.With a solid the oretical foundation,the SVM method is a kind of novel small sample learning method,which can be employed to deal with the problems of highly nonlinear classification and regression.Based on the daily total solar radiation and sunshine duration data in Nanjing in 1981,1996 and 2001,a model of total solar radiation estimation is established by using the SVM method,which is used to forecast total solar radiation in 1982,1997 and 2002.The prediction accuracy of total solar radiation using the SVM method is compared with that obtained by the linear climatological method.Furthermore,the above results are compared with the observed values.According to the simulated results of total solar radiation in Nanjing by using the linear and SVM methods,it can be clearly seen that the errors of total solar radiation predicted by the linear method is relatively larger,and the simulation accuracy changes significantly with different seasons.Nevertheless,the observed values of total solar radiation and the simulated values by the SVM method in Nanjing are basically consistent,and the simulation accuracy of total solar radiation by the SVM method is higher all the year round.Scatter plots of observed and simulated total solar radiation based on the linear method in 1982,1997 and 2002 indicate that when total solar radiation is less than 10 MJ·m^-2·d^-1,the scattered points of prediction values are dispersed.Especially,when the observed values of total solar radiation are less than 5 MJ·m^-2·d^-1,the scattered points on both sides of the fitted line are uneven and the errors are larger.The determination coefficients(R²)between simulated and observed values based on the 1:1 line for total solar radiation based on the linear method in 1982,1997 and 2002 are 0.800,0.859 and 0.838,respectively,and there is significant correlation.On the other hand,the scatter plots of observed and simulated total solar radiation in 1982,1997 and 2002 based on the SVM method show that the scattered points of prediction values are relatively concentrated.The R² between simulated and observed values based on the 1:1 line for total solar radiation based on the SVM method in 1982,1997 and 2002 are 0.894,0.938 and 0.936,respectively,and the correlation is more significant than that obtained by the linear method.The root mean squared error(RMSE) between the simulated and observed values for total solar radiation based on the linear method in 1982,1997 and 2002 are 3.250,2.649,2.925 MJ·m^-2·d^-1,respectively.Based on the SVM method,RMSE of total solar radiation in 1982,1997 and 2002 are 2.353,1.726 and 1.804 MJ·m^-2·d^-1,respectively,which are less than those obtained by the linear method.Total solar radiation calculated by the SVM method can accurately reflect variation of solar radiation in Nanjing,so the method is more suitable for the calculation of actual solar radiation