Abstract: The conflict between urbanization and ecological environment protection is a major challenge for sustainable urban development. This study utilized Theil-Sen Median trend analysis and Mann-Kendall significance test to analyze the vegetation change trends in Ganzhou City from 2000 to 2020. Additionally, it explored the spatiotemporal characteristics of the relationship between urban expansion and urban vegetation changes in Ganzhou City using an improved Urban Vegetation Cover Index (UVCI). Finally, based on the Geodetector tool, this study investigated the impact of nine factors, including natural factors and human activities, on the spatiotemporal distribution of UVCI, to reveal the characteristics of the impact mechanisms of the relationship between urban expansion and urban vegetation changes within urban regions, i.e. urban centre area and expanding area. The results indicated that: (1) From 2000 to 2020, the overall vegetation in Ganzhou City showed a fluctuating upward trend, but certain areas (mainly mining regions) still experienced some degree of degradation; (2) The relationship between urban expansion and vegetation changes in Ganzhou City exhibited two periods of change from 2000 to 2020, characterized by a trend towards coordination between 2000 and 2015, and a gradual deterioration of the relationship from 2015 to 2020. This deterioration was more severe in the urban centre areas of each county compared to the expansion areas; (3) Factor detection showed that temperature, precipitation, and GDP were the core driving factors affecting UVCI. As the level of urbanization increased, the impact of human activities in the expanding areas was gradually intensified. In the future, promoting the coordinated development of urban vegetation and urban expansion in Ganzhou City requires a comprehensive consideration of various factors and the formulation of differentiated strategies to achieve the goals of ecological civilization construction and sustainable urban development.