Abstract: Collaborative promotion of carbon reduction, pollution reduction, green expansion, and economic growth is a key strategic approach to achieve the ‘dual carbon’ goal and promote the comprehensive green transformation of China′s economy and society. Currently, there is no unified evaluation system for the synergistic effects of carbon reduction, pollution reduction, green expansion, and economic growth. This paper, based on panel data of 30 Chinese provinces (excluding the data of Xizang Autonomous Region, Hong Kong, Macao and Taiwan) from 2011 to 2020, uses the coupling coordination model, XGBoost model, and composite system synergy model to measure the synergistic effects of carbon reduction, pollution reduction, green expansion, and carbon reduction, pollution reduction, and green expansion in each province. The modified gravity model, Dagum Gini coefficient, and Theil index are employed to assess the spatial connectivity and regional differences of the synergistic effects across China′s eight comprehensive economic zones. The results show that: (1) There is a significant difference in the level of synergy between carbon reduction and pollution reduction in China, and the overall level of synergy between green expansion and economic growth is relatively low, indicating a synergistic development feature between the two. (2) The average synergy degree of China′s carbon reduction, pollution reduction, and green expansion growth from 2012 to 2020 was 0.0356. Overall, the synergy level is low, revealing a ‘barrel effect’ where the orderliness of each subsystem is constrained by its weakest link, indicating an unstable and uncoordinated state. (3) At the spatial connectivity level, the spatial connectivity intensity of the synergistic effects of carbon reduction, pollution reduction, green expansion and economic growth among different provinces continues to increase, and shows significant spatial proximity. (4) Regional differences in the synergistic effects of carbon reduction, pollution reduction, and green growth across China′s eight major comprehensive economic zones are significant, with the differences primarily originating within the regions. Notably, the regional differences in the eastern coastal economic zones, the middle reaches of the Yangtze River, and the middle reaches of the Yellow River are gradually increasing, while the gap in the rest of the economic zones are decreasing. Research shows that there is still significant room for improvement in the collaborative level of carbon reduction, pollution reduction, and green expansion and economic growth in various provinces of China. Spatial connections between different provinces play a positive role in this process. Therefore, China should deepen regional exchanges and cooperation, leverage the comparative advantages of different regions, and work together to promote carbon reduction, pollution reduction, green expansion, and economic growth, ultimately achieving high-quality economic development.