Packaging size and price have direct impacts on the profitability of manufacturers. The change in packaging price is relatively clear and transparent, while the change in packaging size is not easily detected by consumers. A closed-loop supply chain system composed of a single manufacturer, a single retailer and consumer was studied by describing the demand function related to packaging size and price. In order to make the optimal package sizes decisions, the influence of packaging size on the recovery channel of closed-loop supply chain was studied. The results show that: with the increase in the unit size production cost, the enterprise should supply the small package products as much as possible. When the consumption of the last unit in the large package increased, the enterprise should appropriately decrease the package size of the large package products. Enterprises should choose packaging size strategy flexibly according to their own conditions and external conditions.