Abstract: The optimal maintenance period for repairable product with renewing warranty was researched in behalf of the customer. The concept of product investment cycle (PIC) of the customer was proposed and the product investment cycle was derived on the basis of the warranty policy and the stochastic process theory. Considering the customer cost structure, the cost rate function of the PIC is established and the optimal maintenance period function is derived. A numerical example demonstrates the practical significance of the PIC. The duration of fulfilling warranty reduces the customer's risk of product early failure. Extended warranty prolongs the PIC of customer and may shorten the maintenance period. The product failure rate function has a significant impact on the economical items of the PIC.