A lightweight merchandise distribution system for online group-buying is provided. The distribution system comprises a computer server, a plurality of small distribution centers, and a plurality of delivery entities. The computer server comprises a merchandise sales-prediction module and a distribution center-optimization module. Before a product is featured on a group-buying website, the number of small distribution centers is set up in a densely populated city based on the center-optimization result. The featured product is then pre-allocated to each distribution center based on the sales-prediction result. Each delivery entity comprises a delivery person, a wireless handheld device, and a delivery vehicle. The delivery person preloads the featured products onto the delivery vehicle before receiving any order. The delivery person delivers the ordered product by the delivery vehicle once the purchase order is received from the wireless handheld device.