In the context of the rapid development of the Belt and Road (B&R) Initiative, the continuous transfer of Sino-US trade to the B&R countries is an important means to mitigate the threat of Sino-US trade, and the environmental impact of this transfer should be considered, so as to provide a scientific basis for China’s policy formulation about achieving this possible trade transfer with minimized environmental impacts. This study proposes a multiregional input-output model and analyzes the impact on carbon dioxide (CO2) emissions of transferring the Sino-US trade to the B&R countries for two types of scenarios. The results show the following: (1) A transfer of either the import trade or the export trade increases global and Chinese CO2 emissions by 81.76 Mt and 24.84 Mt, respectively. When both the import trade and export trade are transferred, the increases in CO2 emissions are only 0.22% and 0.26%, respectively. (2) Globally, the changes in international trade-embodied CO2 emissions are responsible for most of the global emission changes, especially the CO2 emissions exported from Russia, India, and many Southeast Asian countries to China. (3) Different from the impact on global emissions, the increases in Chinese domestic production-based CO2 emissions influence China’s total CO2 emissions. Due to the imported CO2 emissions, the consumption-based CO2 emissions are affected to a greater degree and increase by 70.30 Mt, accounting for only 0.86% of the CO2 emissions in 2015. Finally, some policy implications are proposed.