Research on carbon emission efficiency (CEE) is critical for formulating effective climate change mitigation strategies and advancing regional sustainable development. This study provides a comprehensive analysis of the CEE in the Yangtze River Delta (YRD) region, a key economic region in China, from 2012 to 2021. Employing the super-efficiency Slacks-based Measure Data Envelopment Analysis (SBM-DEA) model to measure the static efficiency and the Malmquist index to track dynamic productivity changes, we examine the spatiotemporal evolution across 41 prefecturelevel cities. The results indicate that: 1) Temporally, the regional CEE exhibited a fluctuating upward trend with a V-shaped recovery pattern, achieving an overall growth of 5.8% over the decade. 2) Spatially, the efficiency displayed a distinct core-periphery structure, forming significant clusters of high-value and low-value zones. 3) Regionally, a clear hierarchical gradient was observed: Shanghai > Jiangsu > Zhejiang > Anhui, which is strongly correlated with city size and administrative tier. 4) The spatial agglomeration pattern evolved from fragmented, small-scale clusters to more consolidated, large-scale high-high agglomerations. This transition underscores the positive impact of industrial green transformation and regional integration policies within the YRD, offering valuable insights for low-carbon development planning in other urban agglomerations.