For a serial multi-process manufacturing system under variable operating conditions, the evolutionary mechanism of inventory stockout probability distribution with spare part sharing is introduced. A variable operating condition maintenance decision model for a single equipment is established to obtain the optimal maintenance time of each equipment, and a system maintenance opportunity judgment mechanism is proposed accordingly. Furthermore, combined with the static-dynamic spare parts inventory threshold and the combined-diffused dual time window strategy, a static-dynamic integrated system opportunistic maintenance decision model is developed for each maintenance opportunity. The optimal system maintenance scheme and spare parts inventory are obtained by minimizing the maintenance cost rate within the planning horizon. The case study shows that the static-dynamic combined opportunistic maintenance strategy is more superior in the rolling updated variable operating condition manufacturing environment.