For studying how to apply PHM, analyzed LRU-independent methods and precursor to failure monitoring form modeling point. Utilized the probability density function of MTBF and the LCC of socket for modeling, and introduced simulating method. Then, the relations between single socket LCC of terminal high altitude antiballistic missile weapon system and safety margin or prognostic distance was studied. Finally, introduced how to calculate PHM cost and select PHM methods using example analysis. The simulation result can be used for selecting PHM methods and calculating particular parameters, the conclusion can also direct how to apply PHM in terminal high altitude antiballistic missile weapon system.