Human activities and climate change have a profound impact on the ecological environment of the Northeastern China Tiger and Leopard National Park (NCTL-NP), and exploring the temporal and spatial evolution of the ecological environment quality in this area is of great significance for the sustainable development of the park. In this paper,we selected the enhanced vegetation index (EVI) to replace the NDVI in the original greenness index, and constructed the remote sensing ecological index (RSEI) for the vegetation growing season from 2001 to 2020 based on the original remote sensing ecological index. Then, we analyzed the temporal and spatial variation characteristics of the ecological environment quality and their responses to climatic factors in the three major control areas of potential habitats and main population agglomeration areas based on the pixel scale. The results show that:(1) The ecological environment quality of NCTL-NP has shown a fluctuating and weak downward trend in the past 20 years. After 2015, the ecological environment quality has gradually improved and reached a good level in 2020; (2) The ecological environment quality of each control area in the park has obvious spatial heterogeneity, the quality of the ecological environment in the central part of the eastern core reserve and the southern part of the potential habitat of tigers and leopards is relatively good, while the main population agglomeration areas are relatively poor. (3) In the past 20 years, the ecological environment quality of NCTL-NP has been extremely unstable.The area with an upward trend in the quality of the ecological environment in the future accounted for 60.86%, indicating that the trend of the ecological environment in the future is generally good, but there is still a continuous deterioration trend in some areas. (4) The ecological environment quality of NCTL-NP is mainly affected by precipitation, which has a significant positive correlation with precipitation, and a weak correlation with temperature and sunshine.