[Objective] Andy soil exhibits a substantially diminished water retention capacity primarily attributed to its structural degradation and deficiency in organic matter, which poses significant constraints on the sustainable development of agricultural practices. The objective of this study was to conduct a systematic investigation into the mechanisms through which microbial agents enhance the water retention properties of sandy soil and their subsequent effects on plant growth promotion. [Methods] In this study, three kinds of Bacillus sphaericus were selected as test materials, and the indoor infiltration evaporation test was combined with the field test to comprehensively evaluate the amelioration effect of different microbial agents on sandy soil from the indexes of soil water retention performance, agglomerate composition, enzyme activity and plant physiology. [Results] The experimental results showed that compared with the control, the proportion of large aggregates (>0.25 mm) increased by 23.09% and 32.51% with tri- and bifurcation treatments, respectively; the tri-furcation treatments increased the organic carbon content by 2.96 g kg-1, and the contents of total nitrogen, alkaline dissolved nitrogen, effective phosphorus and quick-acting potassium increased by 21.54%, 61.50%, 312.16% and 30.17%, respectively; The effects of different fungicides on soil enzyme activities varied, and the three fungicides treatment significantly increased the activities of peroxidase and sucrase; the three fungicides treatment significantly promoted plant growth, which was manifested in the significant increase of plant height, root length and underground biomass percentage, and the root crown ratio was increased by 5% compared with the control treatment.[Conclusion] Bacillus inoculant can effectively improve sandy soil and realize the plant promotion effect by improving soil structure, reducing water evaporation and increasing nutrient content. Among them, the three-agent treatment showed a significantly better synergistic effect than the single-agent treatment in plant promotion.