Abstract: An entropy method for optimal decision fusion in multi-sensor systems is set up under fuzzy stochastic circumstances.On the basis of information models for the optimal decision fusion in amulti-sensor system,the concept of fusion entropy is first put foward.The character of fusion entropy is discussed and the entropy concept of optimal decision in multi-sensor systems is then deduced. The influence of the method in the reliability and false-alarm probability of fusion systems is analyzed showing its significance in enhancing the quality of the fusion systems.