The real rate of return of the digital economy as a whole includes not only the direct increase in productivity brought about by digital investment, but also the additional economic benefits generated by the chain reaction of digital investment in the economy, that is, digital spillover. Digital spillover is an unintended or involuntary impact that is independent of the market mechanism and in fact affects other individuals or society as a whole. This paper, based on the unique research context provided by the supply chain and the data of top five customers and top five suppliers disclosed by Shenzhen-Shanghai A-share listed enterprises in China’s capital market from 2007 to 2022, examines the spillover effect and action channels of upstream and downstream digital transformation on corporate value, with a view to confirming whether and how to realize value co-creation through upstream and downstream digital transformation. Empirical testing finds that: Upstream and downstream digital transformation has a positive spillover effect on corporate value, confirming that digital transformation can realize value co-creation; upstream and downstream digital transformation realizes value co-creation through two channels: the differential strategy effect (product differentiation, service differentiation, and image differentiation) and the economies of scale effect (reducing costs, enhancing profits, and improving pricing power). Further, there are situational differences and structural characteristics in the realization of value co-creation through upstream and downstream digital transformation. That is, when the supply-demand allocation is more concentrated, the supply-demand relationship is more stable, and the supply-demand position is weaker, the above positive spillover effect is more obvious. Moreover, the chain structure is characterized by a downstream pulling, the degree structure is characterized by asymmetry, and the time structure is characterized by a long term. This paper provides micro empirical evidence for understanding the macro digital spillover phenomenon, preliminarily verifies the practical effect of value co-creation, deeply explores the value co-creation logic among enterprises, and enhances the understanding on the externalities of digital transformation.