Large-scale complex systems such as industrial equipment and weapons usually go through storage,standby,testing,operation,maintenance and other states in the whole life cycle,and the internal wear rate of equipment is different in different states,which brings new challenges to the problem of remaining useful life prediction of equipment.In view of this,the degradation model of multi-state switching equipment is established based on Wiener process,and the remaining useful life of multi-state switching equipment is derived by combining semi-Markov model and discrete Markov chain model,and a Monte Carlo simulation method is proposed to solve it.In addition,expectation maximization algorithm and maximum likelihood algorithm are used to identify the parameters of the proposed model.Finally,the effectiveness of the proposed method is proved by simulation experiments and practical cases.