Permafrost, which is defined as ground that remains below 0℃ for at least two consecutive years, is an important component of the cryosphere and is vulnerable to climate warming. Global warming has accelerated permafrost degradation, as evidenced by a thickening of permafrost thaw depths, increasing ground surface temperature, and the change from continuous permafrost to island permafrost. Vegetation is a vital component of the permafrost ecosystem and is sensitive to permafrost degradation. The degradation of permafrost leads to changes in the characteristics of permafrost plant communities, such as species composition and diversity and vegetation cover and biomass. The impacts of permafrost on vegetation have become a key topic in the field of climate change research. However, previous studies of permafrost have mostly focused on the distribution of permafrost, whereas there has been little quantitative research on the mechanistic connection between permafrost and environmental factors and the impacts of permafrost degradation on the ecological characteristics of vegetation. Thus, understanding the response of vegetation ecological characteristics to permafrost degradation is vital. In the present study, we investigated plant ecological characteristics and their responses to changes in the permafrost thaw depths on the north slope of the Great Khingan Mountain valley of northeast China. The results showed that there were 85 plant species belonging to 29 families and 55 genera in 30 plots. Angiosperms were dominant, accounting for 97.6% of the total species, whereas there was only one species each of fern and gymnosperm, accounting for 1.2% of the total species. In terms of four life forms, there were 51, 12, 19, and 3 species of hemicryptophytes, phanerophytes, geophytes, and chamaephytes, respectively, accounting for 60%, 14.1%, 22.4%, and 3%, of total species. Of four hydro-ecotypes, there were 50 species of mesophytes, accounting for 58.8% of the total species, whereas hygrophytes, helophytes, and xerophils accounted for 30.2%, 8.2%, and 2.4% of species, respectively. Families, genera, and species of plants reached a maximum at approximately 50-150 cm of the permafrost active layer thickness (ALT). Plant taxa were next most abundant at an ALT > 150 cm, whereas an ALT ≤ 50 was associated with the fewest families, genera, and species of plants. Species of hemicryptophytes showed a significant increasing trend with increasing permafrost melting depth, whereas the numbers of phanerophyte species decreased. Changes in the numbers of geophytes and chamaephytes with a change in permafrost melting depth were not significant. Species of helophytes decreased significantly with an increase in permafrost melting depth, whereas mesophytes showed an increasing trend. Hygrophyte and xerophil species did not change significantly with a change in permafrost melting depth. Collectively, our study results suggest that the study area has a short summer and a long cold winter, and that the conditions conducive to the growth of plants have tended to moderate. This research provides a theoretical basis for predicting trends in the variation of vegetation ecological characteristics against a background of permafrost degradation. The findings are also important for the development and implementation of agriculture and forestry in the permafrost zone. In addition, our observations potentially provide an effective guide for forest management and biodiversity conservation efforts in permafrost areas.