Taking a two-level inventory system in a cross-border e-commerce supply chain composed of "domestic front warehouse-public overseas warehouse" as an example, considering constraints such as free storage periods in overseas warehouses and international shipping, a two-stage calculation method was employed based on the periodic inventory review (T, S) strategy. A two-level inventory cost control model for the cross-border e-commerce supply chain under random demand and uncertain lead time was constructed. Through mathematical analysis, it is found that there is an optimal maximum inventory level that minimizes the total inventory cost in the two-level inventory system under the public overseas warehouse model. Theoretical reference is provided for inventory cost control in cross-border e-commerce.