Based on the data from the surface and upper air observations in Wuhan and numer ical synoptic prediction data from EC during May 1st 2001 to December 31st 2004, the different samples are made. Based on SVM method, crossvalidations are per formed with randomly samples to find the samples with best factors and optimizat ion parameter g, then the models of the cloud amount forecast are built. The sta bility, the forecast and generalization ability of the models are also revealed by crossvalidations. The results of test and realtime forecast show the fore cast ability of the cloud amount forecast models by SVM.