Based on bilateral trade panel data from the fifteen member states of the Regional Comprehensive Economic Partnership (RCEP) from 2002 to 2024, this paper employs an extended gravity model to systematically examine the impact effects and transmission mechanisms of exporting countries' environmental regulation depth on bilateral trade scale. The results indicate that the deepening of environmental regulations significantly suppresses bilateral export scale, a conclusion that remains robust after conducting multiple robustness checks. Mechanism tests reveal that environmental regulation deepening transmits to the export side through three channels: first, it compels high-carbon industries to reduce emissions, leading to a significant decline in per capita CO₂ emissions; second, compliance expenditures crowd out R&D resources in the short term, reducing green patent output and indicating that the innovation offset effect of the Porter Hypothesis is subject to a lag; third, it drives the elimination of backward production capacity and substitution by clean energy, reducing per capita energy consumption. Moderation effect analysis shows that countries with higher financial development levels experience greater short-term export declines under environmental regulation shocks, reflecting the accelerated capacity rationalization effect of financial systems. Heterogeneity analysis reveals pronounced structural differences: exporting countries with lower institutional quality and lower urbanization levels are more severely suppressed by environmental regulations, whereas transparent institutional environments and factor agglomeration levels effectively buffer the compliance shock. This paper supplements the empirical evidence on the trade effects of environmental regulations from the supply-side perspective of exporting countries, providing an experiential basis for coordinating green transition with stable foreign trade development.