Caohai National Nature Reserve is located in the Yunnan-Guizhou Plateau region, which is a typical plateau wetland ecosystem, and in recent years, the ecological quality is facing serious problems due to the influence of anthropogenic and natural factors. In order to monitor the changes of the ecological quality in the area, the Remote Sensing-based Ecological Index (RSEI) was constructed by utilizing five periods of Landsat images in 1994, 2002, 2009, 2016 and 2023, and based on the Annual China Land Cover Dataset (CLCD) classification algorithm combined with samples of land classes adapted to the study area to classify the five periods of remote sensing images, selected 1994, 2009, 2023 improved CLCD data to construct the land use transfer matrix, through the time series of RSEI and the land transfer situation of the ecological quality of the Caohai National Nature Reserve for a comprehensive analysis. The results show that: 1) from 1994 to 2023, the average value of RSEI in Caohai National Nature Reserve continued to increase, the growth rate was fast and then slow, and the relevant protection policy was the main factor affecting the ecological quality of the environment. The middle and high values of the RSEI were distributed in the southwest corner and the east of Caohai from the scattered distribution of the RSEI in 1994 to the western, southwestern, and southern part of Caohai in 2023, and the RSEI has been distributed in the western, southwestern, and southern part. The proportion of “poor” and “poor” grades in the study area decreased year by year, while the proportion of “moderate”, “good” and “excellent” grades decreased year by year, and the proportion of “good” and “excellent” grades decreased year by year. “Excellent” grades showed a rising trend year by year, and the growth rate of RSEI accelerated significantly at the beginning of the establishment of the Caohai National Nature Reserve in 1992 and after the comprehensive management was fully launched in 2015, respectively. 2) Through the difference analysis of the RSEI, the ecological quality of the Caohai National Nature Reserve from 1994 to 2023 mainly focuses on “getting better”, and the area of “getting better” during the 29-year period is 82.092 6 km2, accounting for 87.52%; the area of “getting better” is 87.52%; the area of “getting better” is 87.52%; the area of “getting better” is 87.52%. 87.52%; the area of “deterioration” is 11.7099 km2, accounting for 12.48%. 3) Through the comprehensive analysis of 1994-2023 RSEI difference and land use analysis, the RSEI “getting better” factors mainly consist of grassland and forest land, the RSEI “getting worse” part mainly consists of construction land and cultivated land, and the area of cultivated land in Caohai National Nature Reserve has changed the most, and the area of outflow haschanged the most, and the area of cultivated land in Caohai National Nature Reserve has changed the most, and the area of outflow has changed the most. Cultivated land area changed the most, the outflow area was 74.585 km2, and the cultivated land area was reduced by 59.046 km2, which was mainly converted into grassland, and the quality of ecological environment was significantly improved. However, it is worth warning that the area of construction land increased by 12.570 km2, and there is a tendency of spreading in the eastern part of the Caohai and the surrounding area, so it is necessary to pay attention to the environmental damage caused by the extension to the reserve.This paper combines RSEI and land use changes to quantitatively evaluate the ecological quality of the Caohai National Nature Reserve over the past 30 years, and coupled with a comparative analysis of protection policy time nodes. From the establishment of the Caohai National Nature Reserve in 1992 to the full implementation of comprehensive management in 2015, the RESI increased sequentially, and the number of land categories transferred to grassland and woodland gradually increased, and the ecological quality became better obviously. Compared with the evaluation of wetland habitats using a single indicator, this paper introduces the land transfer matrix combined with the time series of RSEI to comprehensively analyze the ecological environment of the land, and intuitively reflect the reasons that prompted the change of RSEI to be better/worse from the time and space. The results of this study can be an appropriate reference for the ecological management of Caohai National Nature Reserve.