Based on complexit y and nonlinearit y of soil erosion and sediment in small watershed under single rainfall event, the support vector regression(SVR) and method of the principal component analysis(PCA) were used to determine key factors affecting soil erosion and sediment from Wangjiagou watershed under sin- gle rainfall event.Results showed tha t mud runoff depth, peak flood discharge, maximum 30 min rainfall in- tensity, and rainfall amount were key factors affecting soil erosion and sediment in Wangjiagou watershed.An erosion prediction model by SVR was developed based on observed data for 60 rainfall events in Wangjia-gou watershed.The model validation indicated that the model predicted precision reached as much as 86% for60 rainfall events.The research illustrates that SVR provides a new approach to study complexity and non- linearity of soil erosion and sediment in small watershed under a single rainfall event.