Digital technology innovation, as a powerful engine of modern social progress, has changed the production and lifestyle of society at multiple levels and helps to solve urgent social problems such as environmental protection and climate change. Enterprises are the micro foundation of economic operation, and the realization of the “dual carbon goals” requires the joint efforts of enterprises along the supply chain. However, there are few studies on the impact of customer behavior on suppliers’ carbon emissions, especially on the impact of customers’ digital technology innovation on suppliers’ carbon emissions from the perspective of supply chain spillovers. The financial data and supply chain data of listed companies used in this paper are from the CSMAR database and the WinGo financial text data platform. The supply chain relationships of the top five suppliers and top five customers from 2008 to 2021 are selected as sample data to empirically explore the impact mechanism between customer digital technology innovation and supplier carbon emissions. The empirical study finds that customer digital technology innovation has a significant inhibitory effect on supplier carbon emissions, that is, the higher the level of customer digital technology innovation, the lower the carbon emissions of its suppliers, and this conclusion still holds after a series of robustness and endogeneity tests; the supply chain spillover effect shows that customer digital technology innovation can inhibit supplier carbon emissions through the spillover of supply chain funds and the spillover of green innovation in the supply chain; the heterogeneity analysis results show that when customers have the characteristics of non-state-owned enterprises and high-tech industries, or suppliers have the characteristics of executives with overseas backgrounds and non-polluting industries, the inhibitory effect of customer digital technology innovation on supplier carbon emissions is more significant. Compared with previous literature, this study extends in the following three aspects. First, it examines the relationship between customer digital technology innovation and supplier carbon emissions, enriching the research on the economic consequences of digital technology innovation and providing a theoretical basis for customer digital technology innovation to promote its suppliers to reduce carbon emissions. Second, it provides a new perspective for the study of corporate carbon reduction factors from the micro supply chain perspective. Most existing studies are based on the perspective of corporate carbon reduction itself. This paper innovatively explores the role of customer behavior in inhibiting supplier carbon emissions from the perspective of supply chain spillover, expanding the research path of corporate carbon reduction. Third, it enriches the research on supply chain spillover effects. This study finds that customer digital technology innovation can enhance the cooperative relationship between customers and suppliers through two channels: the spillover effect of supply chain funds and the spillover effect of green innovation in the supply chain, providing a theoretical basis for promoting supply chain carbon reduction. This paper reveals to some extent the spillover effect of digital technology innovation in the supply chain, which helps governments and enterprises to formulate more targeted policies and measures under the “dual carbon” background, providing a theoretical basis for promoting the low-carbon development of the supply chain and industrial chain.