Abstract: The clastic rock areas in Guangxi province are distributed widely. There are many geological disasters in these areas. Statistical methods are used to analyze rainfall influence to geological disasters in the clastic rock areas. The factors include the number of rainfall days, rainfall intensity and effective rainfall. Results show that the relation is good between the geological disasters in the clastic rock areas and the rainfall five days before the disaster. The probability of geological disaster is increased greatly when the rainfall intensity is greater than 50mmd-1(rainstorm) or the previous cumulative rainfall is greater than 230mm. The rainfall risk grading standards in the clastic rock areas are determined for warning and forecasting system of geological disasters in Guangxi province.