Abstract: In this paper studed the algorithm to realize the disjoint calculation in multistate system.In the multistate system reliability analysis,often need to execute disjoint calculation of sets,but it is very difficult in multistate system for the component multistate characteristics.The paper first introduces the cube expression method of sets,and sets up relevant operation rules.Based on the rules,given the disjoint algorithm for multistate system.The example in the paper proves that the method is valid.