On the basis of3S and ANN method, by means of RS interpretation, the resources and environment information such as vegetation coverage, exposing rate of rock, relief degree of land surface, the≥25° slope land area of different land use types is obtained. Then early warning for karst rocky desertification in agricultural land during different periods is done in light of economic and social data such as agricultural population density and farmland areas per person as well as reclaimed indexes of land with the BP Algorithm of ANN method. The results show that the analyses of 3S-ANN are consistent with the actual situation. The warning condition of karst rocky desertification in agricultural land increased constantly from 1977 to 2005. The no-warning condition townships decreased from eleven to zero and the severe-warning condition townships increased from zero to nine, but the warning condition in 2005 relieved slightly compared with that in 2007. In light of the prediction with the data in 2005 and 2007, it is concluded that the rocky desertification degrees in Dongmiao, Jiagui, Baoan and Daxing townships will aggravate in 2015, so should pay more attention in the prevention and control in future.