Assuming a supply chain led by the retailer consisted with a manufacturer and a retailer, the manufacturer’s lowcarbon goodwill and the retailer’s promotion can increase the market demand for the products. By supposing that reducing carbon emissions of the manufacturer has a positive effect on its low-carbon goodwill, and that the low carbon emissions is made as a means of product differentiation to deal with the product homogeneity, the profits of the members of the supply chain among the non-cooperation, the cost-sharing contract and the cooperation are compared. And it is found that the optimal carbon reduction level and the optimal promotion level are the highest in cooperation situation, but implementing the cooperative contract is conditional. In the cooperative situation, a profit-sharing contract is designed in order to smoothly implement the cooperative contract.