Based on the super-efficiency SBM model with unexpected output, this study calculated the urban carbon emission efficiency in order to study the regional differences and spatial spillover effects of urban carbon emission efficiency in the Yangtze River Delta. From 2001 to 2020, the highest average of urban carbon emission efficiency in the Yangtze River Delta was only 0.698, with a low overall level and a flat "Inverted-U" evolution trend. Pure technical efficiency became the main factor driving the change in carbon emission efficiency. The Gini coefficient was relatively high, fluctuating in different years and still dominated by growth. The regional differences in urban carbon emission efficiency increased. The contribution of inter group differences among the four provinces （city） was the main source of the differences in urban carbon emission efficiency. The Moran's I index was positive, which indicated that the positive autocorrelation of carbon emission efficiency was significant, and the spatial spillover effect was obvious. The population density, economic level, and technical level had significant effects. The direct, indirect, and total effects of industrial structure, road network density, and foreign capital intensity on carbon emission efficiency did not pass the significance test. Based on the perspective of factor input-output, the study accurately measured urban carbon emission efficiency in the Yangtze River Delta, identified the causes of the differences in urban carbon efficiency, and introduced the "spatial spillover effect" to analyze the mechanism of carbon emission efficiency. This study compensated for the lack of research on the urban carbon emission efficiency in the Yangtze River Delta and provided quantitative support and scientific inspiration for the low-carbon development.
Keywords: Dagum Gini coefficient; Yangtze River Delta; regional differences; spatial spillover effect; urban carbon emission efficiency.