In this study, the relationship between environmental regulations and technological innovation efficiency is empirically examined via panel data from 33 iron and steel enterprises (ISs) in China between 2015 and 2021. The results show that the average “innovation compensation effect” of environmental regulations on the technological innovation efficiency of ISs exceeds the average “compliance cost effect”, thus resulting in a clearly positive net effect. Both the two-sided effects and the net effects vary across different years, geographical regions, and types of property rights. As the quantile of technological innovation efficiency increases, the positive influence of environmental regulations tends to increase. Furthermore, the strengthening of financing constraints and firm competitiveness enhances the positive impact of environmental regulations on the technological innovation efficiency of ISs. Additionally, a double-threshold effect of environmental regulations on the technological innovation efficiency of ISs is revealed in this study. The realisation of the Porter hypothesis occurs when financing constraints and firm competitiveness fall within specific threshold intervals. This research not only deepens our understanding of the relationship between environmental regulations and the technological innovation efficiency of ISs but also provides valuable policy insights for optimising environmental regulations to facilitate targeted improvements in the level of technological innovation efficiency.