Abstract： To ensure the throughput and reduce the operation cost of per unit time, a model for decisionmakings of preventive maintenances was proposed for series production systems with buffers. First, by analyzing the variation of buffer inventories, a periodic maintenance policy was proposed by taking into account the intermediate buffer and failure of upstream and downstream equipment. Based on the descriptions mentioned above, and in view of the characteristics of series production systems, a maintenance cost model of decisionmakings was established with an objective of minimizing total cost of the system over a defined time horizon. Finally, an evolution algorithm to solve the optimal buffer inventories and maintenance time point was built. The results indicate that the model is valid and practical.