The identification of slip surface for a landslide is mainly based on drilling holes combining with experience of engineers. A brief method to identify weak layer or slip surface existing in a slope is presented by analyzing vibrating signals induced by blasting. The vibrating signals is collected from earth surface in the vicinity of blasting center. At first
the theoretical base of the method is briefly described. By analyzing the signals from in-situ testings
we conclude that the number of drilling holes can be reduced; and the precision for identification of slip surface of a slope can be improved by using this method.