To clarify the effects of shrub encroachment on herb communities in alpine meadow on the northern slope of the Lenglongling in the Qilian Mountains of China, four meadows with different shrub encroachment degrees were selected in this area, and the effects of shrub encroachment on the species composition, community characteristics, species diversities, and nich characteristics of herb communities were investigated by using vegetation community survey and classical niche theory. The results show that during the shrub encroachment process, the height and coverage of the herb communities first increase and then decrease, the density shows a fluctuating trend of increase-decrease-increase, and the above-ground biomass increases continuously. The Shannon-Wiener diversity index, Simpson's diversity index, and Pielou's evenness index are significantly (P<0.05) higher in sample plots with light and severe shrub encroachments than in sample plots with non- and moderate shrub encroachments; the Margalef's richness index is significantly higher in sample plots with light shrub encroachment than in sample plots with non- and severe shrub encroachments. Argentina anserina (Linn.) Rydb., Carex parvula O. Yano, Bistorta vivipara (Linn.) Gray, Thalictrum alpinum Linn., and Viola biflora Linn. have relatively high importance values and niche breadths, making them dominant species. There is a certain relationship between niche breadth and niche overlap, species with larger niche breadths are more likely to exhibit higher overlaps in general, but species with smaller niche breadths could also show relatively high overlaps. In sample plots with severe encroachment, species importance values and Levins niche breadths possess relatively high goodness of fit and relatively narrow confidence intervals, with strong correlations, indicating that dominant herbs have a relatively wide range of resource utilization and relatively strong environmental adaptability at severe shrub encroached stage. The herb communities in the alpine meadow generally exhibit low niche overlap, distinct species differentiation, and relatively weak interspecific competition, but niche overlap among dominant species is relatively high, with intense interspecific competition. In conclusion, shrub encroachment in alpine meadows on the northern slope of the Lenglongling in the Qilian Mountains promotes the increase of above-ground biomass and the enhancement of species richness, diversity and evenness in herb communities, but shifts in dominant species may alter the ecological stability of the meadow.