Functional diversity and functional redundancy are crucial to maintaining the stability of a community, but the strength and relative importance of these effects remains poorly understood. In this study, a field manipulation experiment was conducted in an alpine Kobresia humilis meadow at the Haibei Research Station of the Chinese Academy of Sciences from 2007 to 2012, with the aim of gaining insight into the relationship between community stability, functional diversity, and functional redundancy. The experiment used a split-plot design with three clipping levels (stubbled 1 cm, 3 cm, and unclipped) used on the whole plot, and subplots were treated with or without fertilizer (12.75 g m^-2 a^-1 urea + 3.06 g m^-2 a^-1 ammonium phosphate or unfertilized). Our results showed that the community stability monotonously increased with increasing functional diversity and functional redundancy; however, the effect of functional diversity on stability was greater than that of functional redundancy, given that the coefficient of variation of functional diversity under different treatment combinations was greater than that of functional redundancy. Furthermore, the degree of positive correlation between functional diversity and species diversity was stronger than that between functional redundancy and species diversity. We also found a closer positive relationship between functional diversity and community stability than that between functional redundancy and community stability. Although the insurance effect from functional redundancy may improve the stability of a community, the complementary effect of functional diversity on stability appears to be much greater. As such, this result suggests that the relative strength of the effects of functional diversity and functional redundancy on community stability is positively correlated with the degree of variation in functional diversity and redundancy, which confirmed our speculations. Meanwhile, functional diversity is more tightly related to the community stability and can be a better predictor of ecosystem stability than species diversity or functional redundancy. Our study provides a critical insight into sustainable management of rangeland ecosystems.