To address carbon cost pressures from the CBAM and fluctuation in China’s domestic carbon-pricing mechanism, it is crucial to design a carbon quota allocation scheme for China’s steel industry that balances total quantity control and structural optimization. This study comprehensively considers the industry’s LCA and regional heterogeneity, introduces indicators related to “energy transformation contribution”, and employs the maximum deviation method and harmony allocation model to calculate and evaluate provincial quotas and their performance. Results show that: (1) Under the national total quantity control strategy, China’s steel industry carbon quota will be reduced to 1770 Mt by 2030; (2) Calculated via the maximum deviation method, the energy transformation contribution index accounts for 18.95% of the total contribution of all factors, while the LCA index accounts for 46.61%; (3) The maximum inter-provincial difference in carbon quotas reaches 175 Mt, reflecting significant heterogeneity in ecological carrying capacity, resource-allocation efficiency, and emission-reduction potential across regions. This study provides a scientific basis for optimizing China’s unified carbon-market mechanism and guiding the steel industry’s energy transition, and offers a reference for developing countries to address international carbon barriers through regionally differentiated strategies.

To quantify the potential of carbon pricing and green finance to jointly drive deep decarbonization in the building sector, this paper extends the MESSAGEix-Buildings model using a policy-endogenous approach. It incorporates the internalization of carbon pricing and carbon emission costs, as well as mechanisms to relax capital constraints in green finance, into the system optimization framework, thereby enabling the quantification of marginal abatement costs and policy interactions. Using civil buildings in Beijing as case studies, four scenarios were devised for simulation analysis. The results show that: (1) carbon pricing alone can achieve a 11.44% reduction in carbon emissions by 2050, whereas green finance can only alleviate investment barriers and deliver only modest additional emission reductions; (2) when the two policies are implemented in tandem, the joint framework generates complementary price constraints and financial incentives, achieving an additional 4.68% reduction in final energy consumption and a nearly 5.27% saving in total investment compared with the carbon-pricing-only scenario. The study elucidates the complementary mechanism of ‘price constraints and cost incentives’, highlighting the methodological value of an endogenous policy approach, and provides quantitative support for the implementation of carbon neutrality in construction and green finance in megacities.