Abstract: Rural industrial integration is an effective measure to comprehensively promote rural revitalization and accelerate the modernization of agriculture and rural areas. Using data from 30 provinces, autonomous regions, and municipalities across China between 2013 and 2022, this study empirically examined the mechanisms and spatial spillover effects of industrial and commercial capital flowing into rural areas on rural industrial integration. The findings were as follows: First, industrial and commercial capital flowing into rural areas could significantly promote rural industrial integration. This conclusion remained valid after various robustness tests. Second, industrial and commercial capital flowing into rural areas could optimize resource allocation and facilitate the integration of the three rural industries, but it may also exert pressure on collective development in rural areas, thereby having a negative impact on the integration of the three rural industries. Third, there was a significant spatial clustering characteristic of rural industrial integration and the flow of industrial and commercial capital into rural areas, and the flow of capital had a significant positive spatial spillover effect on rural industrial integration. According to the above research, it was recommended to improve policy systems and supervision mechanisms, innovate business, organizational, and cooperative models for rural collective economies and industrial and commercial capital, coordinate differentiated policies for the flow of industrial and commercial capital into rural areas, and establish a networked cross-provincial collaboration mechanism.