3PL warehousing has become an important link between suppliers and retailers in the cross-border e-commerce supply chain. During the COVID-19, product shortage became one of the biggest concerns with the overseas 3PL warehouse integration using ocean shipment. Therefore it has become the focus of the cross-border e-commerce industry and research. Due to the large volume and low-value density, furniture products are generally replenished by ocean transportation. The shortage of such products can be caused by ocean transportation which brings uncertain arrival times and difficult inventory control. This paper, considering the uncertain lead time, uncertain demand, and 3PL warehouse free storage period, introduces a replenishment inventory control model. Utilizing the mathematical dynamic simulation model, it takes refrigerators as a product example into the calculations to prove the validity and accuracy. The experimental results demonstrate that the warehouse free-storage period is a vital factor affecting inventory control for cross-border e-commerce enterprises. When the lead time is uncertain, it is the most optimized solution to use the maximum lead time to determine the maximum inventory.