[Objective] The ecological environmental changes of Zhoushan Island from 2000 to 2020 were dynamically monitored and evaluated in order o provide a scientific reference for the evaluation of the ecological quality of similar island areas. [Methods] Remote sensing images of Zhoushan Island in 2000, 2005, 2010, 2015, and 2020 were selected on the Google Earth Engine (GEE) platform. Wetness, greenness, heat, and dryness were extracted for coupling, and the remote sensing environmental index (RSEI) was obtained. The principal component analysis method was then used to evaluate changes in the quality of the ecological environment of Zhoushan Island. [Results] ① The mean values of RSEI on Zhoushan Island at the five time points were 0.631 2, 0.637 5, 0.611 6, 0.550 3, and 0.502 4, respectively, with a total decrease of 20.41% over the study period. ② The ecological quality of Zhoushan Island exhibited a downward trend over time, with the area of the island having excellent and good ecological quality decreasing by 24.39%, and the area with poor and poorer quality increasing by 19.82%. ③ During the study period, human development activities on Zhoushan Island have increased significantly, land use types have changed, and climate change and human activities have combined to degrade the ecological environment of Zhoushan Island. [Conclusion] RSEI was effectively used to monitor and evaluate the ecological environmental quality of the island. The ecological environmental quality of Zhoushan Island was relatively stable during the early part of the study period, but there was an obvious decline in environmental quality during the later part of the study period, with a total decrease of about 20.41% during the study period.