This paper studies differential game models for the joint carbon emission reduction and promotion in a three-echelon supply chain consisting of a supplier, a manufacturer and a retailer under the low carbon environment. Based on twice cost accumulation, considering product demand affected by the amount of carbon emission reduction,retailer promotion efforts and product retail prices, the dynamic equilibrium strategy and optimal emission reduction track are abtained under conditions of decentralized manners and centralized manners. Numerical examples and sensitivity analysis show that, the amount of carbon emission reduction, the wholesale price of the product and the effort level of supply chain members will gradually increase to a stable value with time, whether it is under the decentralized manners or the centralized manners, but the stable value under centralized manners is larger than that under the decentralized manners. If the impact coefficients of the supplier's and manufacturer's emission reduction efforts to the rate of emission reduction and the impact coefficient of the retailer's promotion efforts to product demand are increased, the amount of carbon emission reduction, the wholesale price of the product, efforts level of supply chain members, profits of supply chain members and the whole system will increase accordingly. The total profits under centralized decision are larger than that under decentralized manners. Finally, the multi-objective cooperative decision method is used to distribute the total profits in this multi-player alliance game model, which improves the overall performance of the whole supply chain system.