Environmental taxes have become an essential tool for regulating pollution emissions. However, there is limited literature exploring the spillover effects of environmental taxes on emission reduction from a 'point-to-line' perspective. This study examines the supply chain spillover effects of environmental taxes levied on upstream and downstream enterprises on the emission reduction of focal enterprises, using data from Chinese A-share listed companies on the Shanghai and Shenzhen Stock Exchange from 2012 to 2021. The results show that: First, environmental taxes levied on upstream and downstream enterprises promote emission reduction in focal enterprises along the supply chain. Second, environmental taxes levied on upstream suppliers have greater supply chain spillover effects on the emission reductions of focal enterprises than those of downstream customer businesses. Environmental taxes levied on upstream and downstream enterprises from different industries have greater spillover effects on the emission reductions of focal enterprises than those levied by enterprises from the same industry. Third, the supply chain dependence of focal enterprises and the technological cooperation with upstream and downstream enterprises strengthen the supply chain spillover effects of environmental taxes. Industry competition weakens the supply chain spillover effects of environmental taxes. The above research conclusions not only reveal the supply chain spillover effects and spillover mechanisms of environmental taxes, but also provide a theoretical basis for improving emission reduction measures from the perspective of the supply chain.