【Objective】Phosphorus is a major element essential for biological growth, but its bioavailability and utilization efficiency in soil are low. Microorganisms play important roles in soil phosphorus cycling. In recent decades, phosphate solubilizing bacteria and microalgae have been widely used as biofertilizers, with great effects on soil phosphorus cycling and the composition and activity of microbial communities. Nevertheless, the combined effects of microalgae and bacteria have been given little attention. This study aimed to explore the effects of the combined application of Bacillus megaterium and Chlorella vulgaris on phosphorus availability and the microbial community in paddy soil. 【Method】In this study, a laboratory cultivation experiment was carried out by using Bacillus megaterium, Chlorella vulgaris, and paddy soils from Jurong, Jiangsu, China, with four treatments, including the application of Chlorella vulgaris alone(A), application of Bacillus megaterium alone(B), combined application of Bacillus megaterium and Chlorella vulgaris(A+B)and the control without application of Bacillus megaterium or Chlorella vulgaris(CK). Specifically, we measured soil pH, contents of Olsen-P, total organic carbon(TOC), and total nitrogen(TN). Also, we determined the soil microbial community composition and diversity using 16S and 18S rRNA gene amplification high-throughput sequencing and characterized the metabolic heat release of soil microorganisms using microthermal analysis.【Result】After 30 days of culture, the soil Olsen-P content of combined application of Bacillus megaterium and Chlorella vulgaris(A+B, 15.92 mg·kg^-1)was significantly higher than that of the control and Chlorella vulgaris alone(A: 14.46 mg·kg^-1, CK: 14.61 mg·kg^-1), with an increase of 9.0% compared to the control(14.61 mg·kg^-1). The combined application of Bacillus megaterium and Chlorella vulgaris also significantly increased the pH, TN and TOC contents of paddy soil. The relative abundance of Bacillus in the soil of the combined application of Bacillus megaterium and Chlorella vulgaris(1.70%)increased by 27.9% compared to that applied with Bacillus megaterium alone(1.33%), and the relative abundance of Chlorella in Chlorophyta of the combined application of Bacillus megaterium and Chlorella vulgaris(3.14%)increased by 3.18% compared to that applied with Chlorella vulgaris alone(3.04%). Also, the combined application of Bacillus megaterium and Chlorella vulgaris significantly increased the metabolic activity and proliferation rate of soil microorganisms. 【Conclusion】 This study showed that the combined application of Bacillus megaterium and Chlorella vulgaris significantly improved the availability of P in paddy soils and the activity of soil microorganisms. This provides practical information for the development and utilization of algae and bacteria-based compound biofertilizers, and a new perspective for improving the phosphorus availability in paddy soils and for alleviating the accumulation of P and reducing environmental risks.