Whether international investment agreements really promote international direct investment has not yet formed a unified conclusion. Based on the panel data of China’s outward foreign direct investment (OFDI) in 130 countries from 2003 to 2017, this paper empirically examines the mechanisms of bilateral investment treaties (BITs), double taxation treaties (DTTs) and treaties with investment provisions (TIPs) from the perspective of the host country. The results show that the BITs and TIPs signed by the host country and China promote China’s OFDI through direct effects, while the BITs and TIPs signed by the host country and other countries attract China’s OFDI through signal effects and institutional complementarity. However, the promotion effect of DTTs is not significant. In addition, if the host country violates the commitments of international investment agreements, it will lead to the decline of China’s OFDI inflow. Further research finds that the promotion effect of international investment agreements on China’s OFDI is more obvious in the period of stable economic development. The role of international investment agreements in attracting China’s OFDI is stronger in developing countries than in developed countries, and the DTTs of developed countries have a stronger inhibiting effect on China’s OFDI.