Abstract: Regarding quantity flexible contract as the research object, two financing methods for downstream enterprises of supply chain are put forward-external financing for supply chain and internal financing for supply chain based on the responsive supply chain formed by a single supplier and a single retailer. By applying the financing methods for the responsive supply chain under the capital constraint and through theoretical evidence, it is concluded that internal financing can deduct the financing cost as well as to stimulate the retailers to order more products and can finally reach the best performance of the supply chain under the condition that the supplier has a good credit.