Increasing green investment is one of the important ways to promote sustainable development in the Belt and Road (B&R) region. We predicted the effects of China’s investments on the CO₂ emission patterns in B&R areas under the scenarios of No-Investment (NIS), Business-as-usual Investment (BIS) and the Strengthening Investment Scenario (SIS) based on the improved Solow model and a CO₂ intensity model. The results reveal that the GDP of B&R region will cumulatively increase by 45.16 and 97.02 trillion USD, and the CO₂ will cumulatively decrease by 44.16 and 79.47 Gt by 2100, respectively, under BIS and SIS, compared with NIS. The cumulative decrease of CO₂ emissions, 44.16 and 79.47 Gt, will lead to global CO₂ concentration decrease by approximately 2.41 mL/m³ and 4.33 mL/m³ in 2100, respectively. Regionally, China’s investments have the most obvious role in promoting the economic development and CO₂ emission reductions of Southeast Asia and its surrounding areas. In the short term (2017-2050), China's investment may lead to a small increase in CO₂ emissions in Southeast Asia and its surrounding areas, India and the Central and Eastern Europe, but in the long term (2017-2100), China's investment will promote the reduction of CO₂ emissions in all regions, especially in Southeast Asia and surrounding areas and the Middle East Central Asia region. This shows that China's investment is conducive to promoting the green development of the B&R regions.