Abstract: This study aims at applying Event Tree Method and Fuzzy Set Theory on the research of the risk analyzing and evaluating in enterprise merger and acquisition. After analyzing the major risks during various stages of enterprise merger activity, the author builds the Event Tree Analysis model and then put forwards the event probabilistic estimation algorithm based on fuzzy set theory. Finally, an evaluation method on the risk of enterprise merger and acquisition comes up with on ascertaining the probability and the crisis consequences of the sequence of events. And in case analysis, well effect of the method above is certified.