This paper empirically evaluates the carbon emission reduction effects of China’s carbon emission trading policy using panel data from 30 provinces from 2005 to 2022, applying the synthetic control method based on LASSO. The study finds that: First, the carbon emission trading policy significantly reduces carbon intensity in pilot regions. Second, the policy effect shows significant regional heterogeneity, with the carbon intensity reduction in Industrial Transition Zones (Chongqing, Hubei, Tianjin) being significantly higher than that in Service-Innovation Hubs (Beijing, Shanghai, Guangdong). The study recommends: 1) Optimizing the design of the carbon emission trading mechanism to enhance policy flexibility; and 2) Strengthening regional coordination to promote balanced policy effects. This research provides empirical evidence for improving carbon emission trading policies and holds important theoretical and practical significance for advancing China’s “Dual Carbon” goals.