In order to solve the problem of variable task requirements in Multi-State System(MSS), the Markov model is extended, and a performance-demand model of multi-state repairable system is derived based on the basic definition of Markov reward model.On this basis, a reliability evaluation method is proposed for the multi-state repairable system considering variable task requirements by certain transformation of reward matrix and transition intensity matrix. The feasibility of the method is verified by using a case.