Abstract: The Yangtze-to-Huaihe river water diversion (YHRWD) project is an inter-basin water transfer project. The construction of the water transfer project has a significant impact on the ecological environmental quality (EEQ) within the project area and the surroundings. To quantitatively assess, monitor, and analyze the temporal and spatial differences of impacts of the YHRWD project on regional EEQ, this study calculates greenness, humidity, heat, and dryness indexes and uses principal component analysis. Eight Landsat OLI_TIRS images are based on the least amount of cloud and during the harvest season from 2013 to 2021 which download from the USGS and Geospatial Data Cloud website. The spatiotemporal change monitoring is determined by comparing the changes of EEQ before, during, and after the construction period of YHRWD project. Respective comparisons are also made with the surrounding areas. The results show that: (1) The mean of RSEI of Lujiang County is 0.739 5 during the study period, and the EEQ is generally good, stable, but slightly decreased. The construction of the project does not significantly affect the EEQ of the whole Lujiang County. (2) The RSEI value of the YHRWD project area during the construction period is 38.70% lower than before the construction period. It still does not improve significantly after construction and back to 84.13%. (3) The RSEI value of the surrounding area (within the 1km buffer zone) decrease by 17.11% on average during the construction period. After the construction, the EEQ gradually recover to 88.28%, which will continue to affect the surrounding ecological environment and the eco-system of the project area has not recovered yet. Although the EEQ in the YHRWD project area is affected by the construction, it has little impact on the surroundings, and the environmental recovery degree after the construction is better. The Lujiang section project not only has a certain guiding significance for the construction, management, and regulation of other sections of the YHRWD project, but also guides the ecological management and regulation of other project areas. This study can provide a reference for ecological environment protection in the process of major project construction and regional spatial planning.