Backgroud Danjiang River Basin (Henan section) is the water source of the Middle Route Project of South-to-North Water Diversion Project, its ecological quality is the important reference for the protection of water sources. The implementation of the Middle Route Project of the South-to-North Water Diversion Project has impact on the Dan River Basin (Henan section), so we should study the changes in ecological quality of water source after the implementation of the project.

Methods This paper chooses the Landsat series of remote sensing images of 1998, 2008, and 2017 as the data source and extracts four indicators information which include the greenness, the humidity, the heat, and the dryness. Then combines these indicators with the principal component analysis method to integrate four indicators information, using the PC1 to construct the remote sensing ecological index (RSEI), and dynamically monitoring the ecological quality and its changes in the Danjiang River Basin (Henan section) in the past 20 years, and combining the existing data to analysis the change reasons.

Results The study results shows that from 1998 to 2017, the ecological quality of the Danjiang River Basin (Henan section) was significantly improved, and the average value of RSEI increases from 0.632 0 in 1998 to 0.636 6 in 2008, and the value reaches 0.699 4 in 2017; From the perspective of spatial distribution, the areas with better ecological quality are located in the mountainous areas where in the western and northern parts of the study area, while the poorer areas are mostly located in the population gathering areas and parts of the cultivated areas. These three groups RSEI data are used to calculate the difference and generate the change monitoring maps. After analyzing the relationship between the changes in the regions and land use conditions, it was found that the regions where ecological quality deteriorated were mainly concentrated in the northern woodland and central urban areas, and the better areas are concentrated in the arable lands in the southeast and central regions, which indicates that the ecological quality of the study area is closely related to the increase in vegetation coverage and the expansion of construction land.

Conclusions In the past 20 years, the RSEI of the Danjiang River Basin (Henan section) has been continuously improved, shows that the overall ecological environment in the study area constantly getting better, but in part of the study area, the ecological environment becomes worse because of the influence of human activity. Using RSEI is a new kind of effective method to monitor the area ecological environment change situations, and the results can provide a reasonable and reliable reference basis for the study area's ecological protection and soil and water conservation in the future.