Abstract: In the context of sustainable development, achieving the synergy of carbon reduction, pollution reduction and green expansion is the general starting point for promoting the comprehensive green transformation of China's economic and social development. As the first region in China to carry out coordinated pollution control, the Beijing-Tianjin-Hebei (BTH) region's effort to promote carbon reduction, pollution reduction and green expansion has important demonstration significance for implementing the "dual carbon" goal and promoting high-quality development in China. Based on the data of 16 indicators of 13 cities in the BTH region from 2000 to 2020, a Carbon Reduction-Pollution Reduction-Green Expansion system was constructed. The spatiotemporal evolution characteristics and driving factors of the synergistic effect of carbon reduction, pollution reduction and green expansion in the BTH region were explored by using the comprehensive index method, coupling coordination degree model and spatial autocorrelation test. The results showed that the composite index of the two subsystems of carbon reduction and pollution reduction in the BTH region showed a fluctuating trend, while the green expansion subsystem showed a trend of first downward followed by steady. The results showed that in the three stages of 2000-2006, 2007-2013 and 2014-2020, the coupling coordination degree was as follows: in the first stage, one city was in mild disharmony, and most cities were on the verge of disharmony; in the second stage, five cities were on the verge of disharmony, and the others were between barely coordination and intermediate coordination; in the third stage, most cities were above barely coordination, and cities with good coordination began to appear. The Moran's indices of the three stages are all negative, indicating that the coupling coordination degree among cities in the study area is unbalanced. However, the absolute values of Moran's indices increase year by year, indicating that the spatial differences in the coupling coordination degree of Beijing-Tianjin-Hebei are becoming smaller, and there is a certain potential for coordinated development in regional carbon reduction, pollution reduction and green expansion.