Abstract: Under the carbon tax policy, it is assumed that consumer demand is jointly influenced by the carbon emission reduction levels of upstream and downstream enterprises and the efforts of low-carbon promotion. Two Stackelberg differential game models are constructed for the long-term joint emission reduction and low-carbon promotion of manufacturers and retailers before and after cost sharing, taking into account the dynamic changes of product carbon emission reduction influenced by the reduction efforts of upstream manufacturers’ emission. The results show that, compared with no carbon tax, the implementation of the carbon tax policy can improve the carbon emission reduction of products and retailers’ profits in the long run, but it will reduce manufacturers’ profits; in addition, when certain conditions are met regarding the carbon tax and the marginal profits of upstream and downstream enterprises, the cost-sharing contract can further improve the carbon emission reduction of products, achieve the Pareto improvement in profits of upstream and downstream enterprises, and broaden the elasticity space of the carbon tax.