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The ecological impact of urban development and population increase is an area of increasing relevance, and urban ecological environment's quality can have a direct impact on people's experience of life. The assessment of urban ecological quality is an important reference for urban ecological protection. Therefore, based on the Google earth engine (GEE) platform, this paper applied a remote sensing ecological index (RSEI) method to study the ecological environment quality (EEQ) changes in Xiamen City in the past 20 years. The four remote sensing indices, Normalized Difference Vegetation Index (NDVI), the heat index (land surface temperature, LST), the wetness index (WET), and the dryness index (normalized difference impervious surface, NDBSI) were first composed. Furthermore, a principal component analysis (PCA) can be implemented to obtain RSEI image. Finally, the EEQ of Xiamen in 2000, 2005, 2010, 2015, and 2020 was evaluated. The results showed that the mean RSEI value of Xiamen in four corresponding years were 0.562, 0.586, 0.564, 0.575, and 0.569, respectively. The area with excellent ecological grade in Xiamen has significantly grown from 310.75 km2 in 2000 to 509.69 km2 in 2020, with an increase rate of 12.21%. The area with excellent ecological grade can be mainly transferred from the good ecological grade. It indicated that the area with the improved EEQ was much higher than the area with the deteriorated EEQ in Xiamen in the past 20 years. The best EEQ among the six districts in Xiamen invariably appears in Tong’an District, which is covered the highest forest area and has the smallest population. On the contrary, the EEQ of Huli District is the worst, mainly due to the high building density, and the large impervious surface areas in Huli District. Despite all this, the average RSEI value in Huli District also shows a steady increasing trend since various construction of urban ecology has been promoted, such the great increase of green space and the continuous reconstruction of the old town in Huli District.
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