In consideration of the features of precipitation enhancement operations on convective clouds in South China, a kind of comprehensive criterion, which is more workable for weather modification activities in grass roots regions, is advanced based on several kinds of branch indexes. The operating grade results are compared with the cumulus numerical simulation results and real precipitation results during the operation experiments period in 2001.Thus the feasibility of the operating grade forecast is certificated, which is significant to the guidance of precipitation enhancement operations on convective cloud.