The entry of platform enterprises into market competition has reshaped the traditional competitive landscape. To investigate potential monopoly risks arising from the cross-market leveraging of platform dominance, an empirical model was constructed by matching cross-platform data from Tmall Supermarket's self-operation channel and Tmall Mall's direct-selling channel. The impact of the expansion of platform self-operation on the sales of seller firms was examined. The findings reveal dual effects—demand expansion and demand substitution—moderated by the market competition environment. In highly competitive homogeneous markets, the platform's segmentation into a self-operated sub-platform and a direct-selling platform is found to alleviate excessive competition, thereby promoting the sales of seller firms. Conversely, in less competitive niche markets, the differential advantage of platform self-operation leads to a decrease in seller firms' sales and a shift of overall industry demand towards the self-operated platform. This substitution effect is shown to primarily impact start-up small and medium-sized Enterprises, resulting in a "Matthew effect" in the allocation of platform resources. The conclusions of this research provide empirical evidence for the formulation of differentiated antitrust regulatory policies for platforms.

self-operated platform  /  cross-boundary competition  /  demand expansion  /  demand substitution