This study constructed a theoretical model to delineate the inherent linkages among TPU, vertical industrial spillovers, and enterprise emission reduction, and empirically examined the spillover effects and underlying mechanisms of TPU changes on enterprise emission reduction using a difference-in-differences model. The study demonstrated that: Every unit increase in the forward spillover effect of TPU reduced the SO₂ emission intensity of downstream enterprise by 28%, and every unit increase in the backward spillover effect reduced the SO₂ emission intensity of upstream enterprise by 16%, This conclusion remained robust after a series of tests; Heterogeneity analysis found that the spillover effect of the decline in TPU on enterprise emission reduction was more significant in domestic-funded enterprise, highly polluting industries, and enterprise in central and western regions; Mechanism analysis showed that the forward spillover of the decline in TPU can affect enterprise emission by stimulating source innovation and improving the energy structure. The backward spillover can affect enterprise emission by promoting the progress of end-of-pipe pollution control technology. Moreover, both forward and backward spillovers can affect enterprise emission by optimizing the factor input structure of enterprise and improving the efficiency of industry resource allocation. The research findings of this paper provided empirical evidence and policy references for facilitating the construction of a new development paradigm and improving the institutional mechanisms for high-standard opening-up.