Karst tiankeng, named in the early 21st century, is a grand negative landform, and its intrazonal habitat conditions are suitable for animal and plant growth and reproduction. In recent years, with the deep excavation of the scientific and aesthetic value of tiankengs, unique habitat characteristics and plant communities of original and mature tiankeng are valued gradually, but the research of degraded tiankeng is still relatively weak. Dazhujing belongs to the typically, heavily-degraded tiankeng in Yunnan, which has higher accessibility and a grassland community in the bottom section of the tiankengs. Therefore, choosing the study area-Dazhujing to analyze the plant communities on the inner and outer parts of tiankeng, it can improve existing theoretical knowledge system and provide significant reference for the ecological restoration of the karst area. This method of field sampling and statistical analysis had been employed to study the characteristics and degree of stability of karst tiankeng's plant community from a qualitative and quantitative point of view. The results showed that:1) There were 35 species belonging to 14 families and 35 genera inside the tiankeng, and 30 species belonging to 14 families and 30 genera outside the tiankeng. The species composition was relatively diverse, with only one co-dominant species; 2) Degraded tiankeng had fragile habitats, and plant diversity outside the tiankeng was higher than that inside the tiankeng, however, the difference was non-significant. In contrast, species evenness outside the tiankeng was significantly higher than that inside the tiankeng; 3) The two communities inside and outside the tiankeng were at very dissimilar levels, which had different and diverse structures and significantly different habitats; 4) The plant communities inside the tiankeng had a non-significant positive inter-specific association, were loose, independent, and at the positive succession stage. However, a negative correlation was found between the plant communities outside the tiankeng, which were at an unstable stage; 5) The stability analysis showed that there was still a gap in community stability, which indicated that the ecosystem of the degraded tiankeng was still fragile.