Based on the systematic GMM and intermediation model, the impact of China's direct investment on the green total factor productivity (GTFP) of the Belt and Road Initiative (BRI) countries are examined from the data of 48 countries during the period of 2008-2019. The results show that China's direct investment can significantly contribute to GTFP in BRI countries through the mediating mechanisms of scale, structural and human capital effects. Of these, the main one is the scale effect. In addition, the scale, structural and human capital effects all positively moderate the green driving effect of China's direct investment in BRI countries, while the technology effect weakens the process.