For researching transition process between each state and combination explosion problem of multi-state component, reliability evaluation of complex equipment is carried out, and Markov process is used to establish the transition process between each state. The probability function of the component in each state can be used to determine by Laplace transforming and inverse Laplace transforming. Thus, reliability assessment models of multi-states components under different maintenance methods are established. The reliability indexes under different maintenance methods are given. Taking control unit as example, the simulation analysis is analyzed. From the results, it’s obvious that conditional based maintenance maintains an element/system at a higher level of reliability comparing to that of perfect repair and imperfect repair.