Abstract: For a two-echelon supply chain system consisting of single-supplier and multi-retailers,the inventory routing problem of centralized supply chains is considered.To reduce the cost of the whole chain,a region partition algorithm for the retailers is redesigned.Based on this,the relationship of the replenishment interval between the retailers and the suppliers is determined.By using interval ratio vector,a new integer-ratio policy is designed.Through a particular theoretical analysis,it is proved that this strategy is the optimal one.Numerical experiment results show that this strategy is evidently better than others.