Abstract: Crops in saline-alkali soil were subjected to low survival rates and poor growth due to saline-alkali stress. Increasing the number or variety of functional microorganisms in saline-alkali soil can significantly promote the growth of plant. To change the current situation where saline-alkali soil was not conducive to the growth of crop, this study analyzed the microbial community structure of saline-alkali soil and isolated functional microorganisms with growth-promoting effect. A multifunctional composite microbial agent was constructed by mixing existing antagonistic bacteria with isolated growth-promoting bacteria, and its growth-promoting effect on mung beans under saline-alkali stress was studied. The soil microbial community structure was analyzed through high-throughput sequencing. The two strains were identified by molecular biology methods. The phosphorus and potassium solubilization ability of strain SI-1-3 were verified through corresponding culture media. The Salkowski colorimetric method was used to determine the production of IAA (indole-3-acetic acid) product and the spectrophotometry was used to determine the secretion of GA (gibberellin). The inhibitory capability of antagonistic Y-2 against pathogenic bacteria was determined using the petri dish confrontation method, and the compatibility experiment between strains was conducted using the cross line method in a petri dish to ensure the rationality of the composite microbial formulation. The saline-alkali conditions of the tested soil in the pot experiment were determined by measuring the saline-alkali tolerance range of the composite microbial agent. Pot experiments was used to determine the effects of the compound strains on the emergence rate, incidence rate, growth indicators, physiological and biochemical indicators of mung beans in order to verify the growth promotion effect of the composite microbial agent. The results showed that Proteobacteria, Actinobacteria, and Firmicutes were the dominant bacterial communities in soil samples, while Ascomycota had the highest proportion of fungal communities. We isolated a bacterium with a higher isolation frequency from the dominant strains and named it SI-1-3. It has been identified as Bacillus subtilis, with the ability to dissolve organic phosphorus and decompose potassium elements, and can secrete indole-3-acetic acid and gibberellin. According to the phylogenetic tree, it can be seen that the antagonistic strain Y-2 is Pichia membranifaciens. Through plate experiments,it was found that antagonistic bacterium Y-2 had a significant inhibitory effect on Fusarium raminearum and Pyricularia oryzae Cav. There was no antagonistic effect between the two strains through compatibility tests, and they could be co-cultured to construct a composite microbial formulation with a volume ratio of 1:1. After identifying the saline-alkali tolerance of the composite bacterial agent, it was found that the growth of the strain was best in PDB medium with a pH value of 8.5 and NaCl concentration of 5%. Therefore, a pH value of 8.5 and NaCl concentration of 5% were selected as the saline-alkali stress conditions for subsequent experiments. After planting mung beans in saline-alkali soil and treating them with the composite microbial agent, it was found that under saline-alkali stress conditions with pH 8.5 and NaCl concentration of 5%, the composite microbial agent had a certain promoting effect on the growth of mung beans. In the pot experiment, when compared with the control group, the emergence rate of mung bean increased by 7.44%, the incidence rate decreased by 82.37%. Additionally, the root length, plant height and fresh weight of stem and leaf of mung bean being treated by the composite microbial agent increased by 75.24%, 64.33% and 66.67%. At the same time, the chlorophyll, soluble sugar and soluble protein content of mung bean seedlings increased by 71.63%, 64.21% and 77.87%. This composite microbial agent has a promoting effect on plants, thus providing an effective biological control method for the improvement of saline-alkali land and agricultural development, and is expected to be further developed as a microbial resource in specific environments.