Optimizing resource allocation is the action-oriented of the Belt and Road initiative and the essential requirement for promoting high-quality development in the countries along the route. This paper evaluates the impact of the Belt and Road initiative on the resource allocation efficiency of the countries along the route and its mechanism of action using the multiple period difference-in-differences model. The research found that: The Belt and Road initiative helps optimize the allocation of capital and labor in the countries along the route, especially in the area of labor allocation efficiency. The initiative improves the efficiency of capital and labor allocation through policy communication, facility connection, smooth trade and people-to-people communication, but there is a slight distortion in capital allocation through capital financing. Low-and middle-income countries and Asian countries benefit more significantly in capital and labor allocation efficiency. This paper responds positively to the “threat of transferring excess capacity” faced by the Belt and Road initiative from the international perspective of resource allocation and also broadens the policy ideas for further promoting the Belt and Road construction.