Abstract: How to estimate the probabilities of different scenarios scientifically in the beginning of emergency is a premise and key problem for emergency decision making. This paper proposes a method for estimating scenario probabilities by combining the subjective and objective data. In this method, firstly, the history cases are screened according to the calculated similarity degree between history cases and the current emergency event. Then, the objective scenario probabilities are calculated according to the statistics of scenario of similar cases. Furthermore, the subjective scenario probabilities are estimated according to the weighted average result of expert judgments. Moreover, scenario probabilities are obtained by integrating the subjective and objective scenario probabilities. Finally, a numerical example is used to illustrate the feasibility and significance of the proposed method.