A pot experiment was conducted to investigate the effects of inoculation of Glomus mosseae on the growth and nutrition uptake of Melilotus albus Desr. under water stress and/or phosphorus deficiency conditions. The pot trials include two levels of soil relative water contents (35% and 65%) and three levels of phosphorus (0, 25, 50mg·kg^-1), either with inoculation of Glomus mosseae or without inoculation. The results show that the water stress does not inhibit the mycorrhizal infection of Melilotus albus. However, a high level of P in soils (50mg·kg^-1) under water stress would significantly inhibit the mycorrhizal colonization. The inoculation of Glomus mosseae significantly increases the uptake of N and P in Melilotus albus and consequently alleviates the negative effects of Melilotus albus under water stress. The highest biomass of the shoot and the root of Melilotus albus is recorded in the treatments of inoculation in 50mg P·kg^-1 soils. In addition, the inoculation of Glomus mosseae significantly enhances the coefficient of the water use of Melilotus albus under water stress or not. The results suggest that the inoculation of arbuscular mycorrhizal (AM) fungus may be a promising approach for increasing the growth of grass and enhancing the revegetation of the degraded grassland in arid and semi-arid regions.