According to the statistics results of the rainfall return period,in recent years after Wenchuan earthquake, the has great correlation with the rainfall intensity of big storms and super storms hitting instead of rainfall of design criteria of debris flow control projects. therefore,the method of exceedance probability analysis,in other word,the probability beyond the rainfall frequency of design criteria of the debris flow control projects failure,was proposed on the assessment of reliability of debris flows control projects. the model based on the rainfall frequency statistics was established grounding on the method of mathematical statistics and taking for example of debris flow control projects in Dujiangyan County, Chengdu City.