A model of constant probability event is constructed rigorously in event space of PSCEA. It is showed that the numericalbased fusion and the algebraicbased fusion have a consistent result when the weight is regarded as a constant probability event. From the point of view of algebra, we present a novel similarity measure in product space. Based on the similarity degree, we use a similarity aggregation method to fusion experts’ evaluation. We also give a numerical example to illustrate the method. A is a graph of constant probability event is constructed rigorously in event space of PSCEA. It is showed that the numerical based fusion and the algebraic fusion have a consistent result when the weight is regarded as a constant probability event. From the point of view of algebra, we Based on the similarity degree, we use a similarity aggregation method to fusion experts’ evaluation. We also give a numerical example to illustrate the method.