China's economic development has entered the stage of capital export from commodity export. However, in the process of continuous export of China's OFDI, the institutional environment of the host country has gradually become one of the important factors affecting China's OFDI, and the institutional difference between China and the host country will also have an important impact on China's capital export. Based on sample data of China's OFDI to 34 countries along the Belt and Road from 2006 to 2019, the investment gravity model is constructed and the fixed effect regression method is used to empirically analyze the impact of economic, political and legal institutional differences on China's direct investment in countries along the Belt and Road. The results show that the legal institutional difference has the greatest negative effect on China's direct investment in the countries along the Belt and Road, the negative influence of political and economic system difference decreased successively. China's direct investment in different types of countries along the Belt and Road is also significantly heterogeneous due to institutional differences. For countries along the Belt and Road with different economic systems and levels of economic development, differences in legal institution have the greatest impact on China's OFDI. Moreover, the restraining effect on China's direct investment in transition countries and high-income countries along the Belt and Road is significantly greater than that on non-transition countries and low and middle income countries. From the perspective of countries with different levels of resource abundance, legal institutional difference has no significant impact on China's direct investment in resource-rich countries along the Belt and Road. However, it has a significant negative impact on the direct investment of resource-deficient countries along the Belt and Road.