Straw returning is an effective practice for improving soil quality and increasing soil nutrients. However, the effect of straw returning on soil phosphate fractions and phosphate-solubilizing microorganisms (PSM) needs to be clarified. Here, we studied the variation of soil properties, soil phosphate fractions, and microbial communities at 0–40 cm soil layer under four treatments (S0 (0 kg/ha straw), S1 (3000 kg/ha straw), S2 (6000 kg/ha straw), and S3 (9000 kg/ha straw)). Soil properties were measured by conventional methods; soil phosphate fractions were measured by the Bowman-Cole method, and soil microbial communities were determined by high-throughput sequencing. The results showed that total phosphorus (TP), total organic phosphorus (TOP), and total inorganic phosphorus (TIP) increased by 16.16–59.52, 53–73.4, and 18.7–45.54% in S1, S2, and S3 compared to S0. The Chao1 (community richness) and Shannon (community diversity) index of bacteria and fungi were significantly higher in S1, S2, and S3 treatments than in S0. Redundancy analysis (RDA) results showed that the contribution of TOP, TIP, and soil organic matter (SOM) to the relative abundance of microbes were 84.20–94.80, 83.20–94.40, and 89.20–94.10%, respectively, which was significantly higher than that of other soil variables (field moisture capacity (FMC), soil porosity (SP), soil bulk density (SBD), pH, electrical conductivity (EC), cation exchange capacity (CEC), residual phosphorus (RP), TP, available phosphorus (AP)). Overall, long-term straw returning can alter the soil phosphate fractions by improving TOP, TIP, and SOM contents, thus effectively enhancing the abundance of soil microorganisms in 0–40 cm soil, especially the abundance of PSM in the surface soil. [ABSTRACT FROM AUTHOR]