To clarify the role of arbuscular mycorrhizal (AM) fungi in enhancing stress resistance in Leymus chinensis, the effects of AM fungi on the growth and physiological metabolism of L. chinensis under saline-alkali stress were investigated by conducting controlled pot experiments. The results showed that saline stress significantly reduced the colonization rate and colonization intensity of AM, and that the inhibitory effects of alkali stress were considerably stronger. Inoculation of Glomus mosseae enhanced the biomass and photosynthetic pigment contents (chlorophyll a and b and carotene) of L. chinensis seedlings under stresses. With an increase in saline-alkali stresses, there was a greater accumulation of Na⁺, but K⁺ uptake was suppressed. Inoculation with AM fungi reduced the accumulation of Na⁺, reduced the decreases in K⁺ content, and enhanced the content of NO₃^-, thereby improving the ion balance of L. chinensis seedlings. Under alkali stress, the contents of citric acid and malic acid were increased, and under saline stress, malic acid content was significantly increased. The activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase were significantly increased by inoculation with AM, thereby enhancing the scavenging of oxygen free radicals by the host plants. The research results show that due to the high pH value, the effects of alkali stress on the mycorrhizal infection were stronger. Inoculation with AM fungi significantly enhanced the stress resistance of L. chinensis seedlings. The mechanism of stress resistance also differed according to stress type. On the one hand, the results provide a scientific basis for the application of L. chinensis to saline-alkali degraded grassland and as a bacterial fertilizer. On the other hand, they also provide the necessary data for elucidating the response and feedback of the L. chinensis-AM symbiosis to saline-alkali stress.