Tundra vegetation of the Changbai Mountains is undergoing significant changes. In the alpine tundra on the western slopes of the mountain, the area of distribution of shrubs is shrinking and the importance of shrubs as dominant plant species is reducing significantly. This study analyzed changes of dominant plant species in the shrub tundra, distribution pattern variations of shrubs and characteristics of shrub community structure at different elevations using plot survey data, revealed regional differentiation of degradation in shrub tundra and the degradation mechanisms of shrub communities. The results showed the following: (1) The shrub community in the alpine tundra on the western slopes has been severely degraded. Various herbs have invaded the area and became the dominant species. Five herbs and two shrub species were the dominant species of alpine tundra, which indicated a decrease in the number and importance value of dominant shrub species compared to the results of the survey conducted in 1979. The aggregated distribution was the dominant pattern of distribution of the seven dominant species, whereas the distribution of each dominant species occurred in separated patches; the shrub tundra faced fragmentation. In shrub communities of alpine tundra, herbs appeared and gradually became dominant. The herbs were taller than the shrubs in alpine tundra at lower elevations, and the species composition and community form were nearing those of the herb-shrub tundra. (2) Shrubs were widely distributed at different elevations, but their spatial distribution patterns were distinct. Below 2300 m a.s.l., the distribution of shrubs appeared aggregated, especially at elevations below 2100 m a.s.l. The shrubs did not aggregate above 2300 m a.s.l. (3) Regional differentiation of the degraded alpine tundra on the western slopes was significant. Below 2100 m a.s.l., the number of herbs was more abundant than that of shrubs, and the coverage and height of the shrubs were decreased; so the degradation is the most serious in this region, which developed into herb-shrub tundra. Between 2100 and 2300 m a.s.l., the degradation was significant, but the number of shrubs were more abundant than that of herbs; this region developed into shrub-herb tundra. Above 2300 m a.s.l., the degradation of shrubs was not significant and shrub tundra was preserved. It can be inferred that the degradation mechanism of the shrub tundra includes two aspects: herb invasion of the shrub tundra, resulting in interspecific competition, and environmental changes of tundra zone, which could be attributed to global climate change.