Green supply chain management has received increasing attention as consumers have become more environmentally conscious. Manufacturers are making green investments to meet consumers’ demands, while retailers in different markets often engage in cooperative promotion to attract more consumers. This study develops game theoretic models for investigating cooperative promotion for two cross-market firms with different channel structures, i.e., decentralized and centralized. The manufacturer determines the wholesale price for the retailers and the green investment of a product, and the retailers determine the promotional effort and retail price. This study finds that whether the firms join in cooperative promotion mainly depends on the wholesale price, as well as the impacts of the price, green investment, and cooperative promotional activities on the demand. When the wholesale price is relatively low, the retail price of the decentralized green supply chain must be lower than that of the centralized green supply chain. On the contrary, the difference in the retail price between the two green supply chains varies with the impacts of green investment and cooperative promotional activities on demand. In addition, due to the influence of channel structure, the contribution to cooperative promotion of the centralized supply chain is more than that of the decentralized supply chain with the most given conditions. Moreover, as the impact of cooperative promotional activities on demand increases, the centralized green supply chain does not necessarily result in higher profits than the decentralized green supply chain.