Abstract: Promoting the synergistic enhancement of pollution reduction, carbon mitigation, green expansion and economic growth is a key task in achieving a comprehensive green transition in economic and social development. This study has revealed the spatio-temporal evolution characteristics, spatial clustering patterns, causes of regional disparities and spatio-temporal heterogeneity of driving factors underlying the synergistic efficacy in Chinese cities from 2004 to 2021. The results show that: (1) The synergistic efficacy index exhibited an upward trend, with a mean increase of 285% and year-on-year improvement, while the overall regional disparities expanded. The spatial transition pattern largely followed a 'northeast-southwest' structure, and spatial distribution tended toward balance. (2) Spatial clustering was dominated by HH-type and LL-type agglomerations with their proportions increased from 28% to 33% and decreased from 54% to 37%, respectively, forming an "east-high, west-low" gradient distribution. (3) The overall disparity in synergistic efficacy showed no significant change. Differences mainly stemmed from inter-regional disparities, with the largest gap observed between eastern and central regions (mean value 0.453), and the smallest disparities were between central and western regions. Eastern regions exhibited relatively higher intra-regional imbalance. (4) Per capita carbon dioxide emissions and per capita electricity consumption generally had a negative impact on synergistic efficacy, accounting for approximately 50% and 75% of the effect, respectively. In contrast, per capita green space and fixed capital stock showed positive effects, with fluctuations strengthening by 6%-8%. The spatial heterogeneity of per capita electricity consumption and per capita green space increased, while that of per capita carbon emissions and fixed capital stock decreased. Finally, the study proposes countermeasures focusing on differentiated regional governance, cross-regional collaboration, and dynamic factor regulation.