[Objective] The effects of microbial inoculants on soil water-retention capacity and plant growth-promotion mechanism in desertified soil were explored in order to provide references for water-retention capacity improvement and sustainable agricultural development. [Methods] Three Bacillus spp. were used. By combining indoor infiltration evaporation experiments with field experiments， the effects of different microbial inoculants on desertified soil were comprehensively evaluated using indicators such as soil water retention performance， aggregate composition， enzyme activity， and plant physiology. [Results] Compared with the control group， the triple and dual bacterial inoculant treatments increased the proportion of large aggregates （0.25 mm） by 23.09% and 32.51%， respectively. The triple bacterial inoculant treatment increased the organic carbon content by 2.96 g/kg， and the total and alkali-hydrolyzed nitrogen， and available phosphorus and potassium contents by 21.54%， 61.50%， 312.16% and 30.17%， respectively. The effects of different bacterial inoculants on soil enzyme activity vary. The triple bacterial inoculant treatment significantly increased peroxidase and sucrase activity and significantly promoted plant growth， which manifested as a significant increase in plant height， root length， proportion of underground biomass， and the root cap increased by 5.0% compared with the control treatment. [Conclusion] Bacillus inoculants can effectively improve desertified soil and achieve growth-promotion effects by improving the soil structure， reducing water evaporation and increasing nutrient content. Among them， the triple bacterial inoculant treatment showed a significantly improved synergistic effect than a single bacterial inoculant treatment in promoting plant growth.