The Urumqi Metropolitan Area, situated in the arid northwestern region of China, faces a particularly fragile ecological environment. Monitoring and evaluating its ecological quality are crucial for sustainable regional development. This study focuses on the Urumqi Metropolitan Area, utilizing the Google Earth Engine (GEE) cloud platform to screen Landsat images from April to September in 2000, 2010, and 2020. A Remote Sensing Ecological Index (RSEI) is constructed to dynamically monitor ecological quality in the study area. Additionally, the Standard Deviational Ellipse (SDE) method is employed to analyze the spatial expansion characteristics of the ecological environment. The results reveal: (1) Temporally, the RSEI increased from 0.307 to 0.343 between 2000 and 2020, indicating an overall improvement in ecological quality. (2) Spatially, ecological quality exhibits significant differences, with higher values in the southern and central regions and lower values in the north. Monitoring results show that from 2000 to 2020, the area experiencing environmental deterioration (44.50%) was smaller than the area showing improvement (55.50%), suggesting an overall trend of environmental quality enhancement. (3) Based on changes in the standard deviation ellipse and centroids of different ecological classes, the overall ecologically better regions in the study area exhibit an east-west orientation, with SDE centroids shifting southeast. This study focuses on the spatio-temporal changes and spatial expansion characteristics of ecological environment quality in the Urumqi Metropolitan area located in the arid region, which is of significant practical and referential implications for the achievement of sustainable urban development.