The optimal design of environmental instruments demands a balance between environmental enhancement and economic growth. Utilizing microdata from the China Environmental Statistics Database and the China Industrial Firm Database, this study employs the difference-in-differences (DD) methodology to explore the dual effects of the SO₂ Emissions Trading Scheme (ETS) on the environmental and economic performance of micro-firms. The findings suggest that: (1) The SO₂ ETS not only induces emission reduction effects among firms in pilot areas but also improves their industrial added value. (2) The SO₂ ETS exhibits heterogeneous impacts across firms of diverse ownership, export status, and size. (3) While the SO₂ ETS prompts firms to advance technologically, boosting desulfurization capacities and subsequently enhancing total factor productivity, it also inadvertently results in companies offsetting some environmental compliance costs by curtailing employee wages.