From the aspect of inventory control, supply-hub is an innovative operation mode that vendor managed inventory (VMI) mode can adapt to supply logistics of components in assembly system. In the VMI mode, suppliers themselves determine their own safety stock and replenishment quantities according to their own production costs, inventory holding costs and other factors. However, there are some factors such as suppliers’ capacity constraints and rising capital cost, which will lower its safety stock level in supply-hub to alleviate their problems, so there are certain risks in practical operation if inventory control of components in supply-hub is completely given to the suppliers. As a result, manufacturers will always require a minimum safety inventory of suppliers’ components in supply-hub, and they will set lower bound safety inventory for materials or components provided by each supplier. In many assembly supply chain, the lower bound safety inventory in supply-hub is generally set to be the average consumption of materials or components within two weeks based on experience [1]. But there is little literature which proves that lower bound of safety inventory is reasonable in theory.