Abstract: To support enterprises in achieving low-cost carbon compliance during the 2024—2026 expansion and transition period of the iron and steel industry in China's carbon market,an optimal compliance cost model incorporating carbon emission intensity coefficient, carbon quota surplus and deficit volume as well as carbon price is established in accordance with the latest carbon quota allocation rules issued by the Ministry of Ecology and Environment. Three typical types of iron and steel enterprises including low-emission enterprises （S₁）, medium-emission enterprises （S₂） and high-emission enterprises （S₃） are selected for simulation analysis. The results indicate that S₁ enterprises obtain carbon quota surpluses due to their superior emission performance against industrial benchmarks with the carbon emission intensity deviation degree higher than 20%. S₂ enterprises with a deviation degree ranging from -10% to 15% face minor carbon quota deficits, while S₃ enterprises with the deviation degree lower than -10% bear prominent pressure for quota supplementation. Compared with three carbon trading strategies of annual supplementary purchase, one-time supplementary purchase and over-purchase strategy, the one-time supplementary purchase strategy locks the low carbon price of 85 yuan per ton in 2025. It effectively reduces capital occupation and total compliance costs of S₂ and S₃ enterprises, with cost savings of 1.393 5 million yuan and 4.455 million yuan respectively, which presents the optimal economic efficiency. Based on the research findings, differentiated compliance schemes are proposed at the enterprise level,a collaborative trading platform is suggested to be constructed at the industrial level, and improvements on quota allocation systems and supporting carbon financial mechanisms are advocated at the policy level. This study provides practical approaches and decision-making references for the efficient low-carbon transformation of the iron and steel industry.