Functional diversity and functional redundancy are two components of species diversity, and are also two important factors that affect the stability of a community. The effects of functional diversity and functional redundancy on the community stability were analyzed based on the estimation of functional diversity, functional redundancy, species diversity, community stability, and their correlations of plant populations under different water and salt gradients The results revealed that:(1) The functional diversity, species diversity, and community stability of plant populations in high and moderate water and salt gradients were significantly higher than those of in low water and salt gradients (P < 0.05). (2) For populations in high water and salinity gradient, the correlation coefficient between functional diversity and species diversity was lower than that of between functional redundancy and species diversity, moreover, the correlation coefficient between functional diversity and stability was lower than that of between functional redundancy and stability. However, the correlation coefficients of populations in moderate and low water and salinity gradients were contrary to those of in high water and salinity gradient. (3) The standardized partial regression coefficients of functional diversity were greater than that of functional redundancy of communities in moderate and low water and salt gradients. (4) In the canonical correspondence analysis, the water and salt content of soil could explain 22.7% and 1.3% of the total characteristic root, respectively. (5) The stability was highest in plant communities in high water and salt gradient, with the stability rate near 20/80, whereas populations in low water and salt gradient had the lowest stability, with the stability rate far from 20/80. These results were consistent with those of estimated by the improved Godron Stability Test Method and Population Density Variance Coefficient Method. In summary, both of the functional diversity and functional redundancy could enhance the stability of plant community, and their effects were dependent on their relationships with species diversity which provided evidence for the redundancy hypothesis of plant communities in the temperate arid desert region. The stability, functional diversity, functional redundancy, and species diversity of plant communities were much more affected by soil moisture, but less by soil salinity.