Digital transformation is not only one of the important internal driving forces for enterprises to maintain competitive advantage, but also one of the singificant driving forces for empowering the innovation networks. Based on the patents and citation data of listed companies from 2007 to 2022, the impact of digital transformation on downstream enterprise innovation through the spillover effect of innovation chain was examined. The results show that digital transformation significantly promotes the innovation level of downstream enterprises. Moreover, in the samples of state-owned enterprises and regions with low levels of intellectual property protection, the impact of digital transformation on the innovation of downstream enterprises is greater. Mechanism analysis shows that the knowledge spillover effect is an important mechanism for digital transformation to promote the downstream enterprise innovation. Further analysis shows that digital transformation in different dimensions has different impacts on the innovation of downstream enterprises. Among them, digital transformation in the technology and platform has a more significant impact on the downstream enterprise innovation, and digital transformation also has a positive impact on the innovation efficiency, innovation quality and total factor productivity of downstream enterprises. These conclusions enrich the relevant research on enterprise digital transformation, and provide important practical references for enterprises to actively integrate into the innovation network.