Stable foreign trade is a crucial foundation for promoting high-quality development of China’s external trade. The construction of a unified national market can help stabilize corporate exports, primarily through reducing institutional costs and expanding and improving consumption. This positive effect is more pronounced among small and medium-sized enterprises compared to large enterprises, and it is also more evident in regions with higher levels of local protectionism. From the perspective of market types, the unified national markets for goods, labor, and capital all support stable exports, with the goods market exerting a relatively stronger influence. Therefore, efforts should be made to simultaneously eliminate local protectionism and market segmentation while improving the institutional rules of the unified market, accelerate the smooth flow of factors and goods across broader areas, continuously deepen relevant institutional reforms, and implement targeted policies based on differences in enterprise scale and regional market environments to enhance the precision and effectiveness of policy measures.