Using Chinese A-share listed companies from 2011 to 2023 as the sample, this paper examines the effect of customer digital technology innovation on supplier firms’human capital upgrading from a supply chain perspective. The results show that digital technology innovation has a contagion effect across supply chains, and customer digital technology innovation promotes supplier human capital upgrading. Further analysis reveals that enhancing the innovation of supplier enterprises and improving supplier debt financing are the key mechanisms through which customer digital technology innovation facilitates supplier human capital upgrading. Heterogeneity tests indicate that the positive effect of customer digital technology innovation on supplier human capital upgrading is more pronounced when the customer’s importance to the supplier increases (e.g., high supplier dependence on the customer, intensified industry competition), the supplier operates in a high-tech industry, or is located in eastern China. Additionally, there is a substitution effect between common institutional investors in the supply chain and customer digital technology innovation in promoting supplier human capital upgrading.