Abstract: Long-term straw return can input abundant nutrients into the soil. By exploring the effects of different amounts of straw return on the physicochemical properties and fungal diversity of paddy soil, we aim to provide scientific evidence for the rational utilization of crop straw. The experiment set up four different treatments: no straw return (S0), half straw return (S1), full straw return (S2), and 1.5 times straw return (S3). Soil samples were taken from the 0−20 cm layer after rice harvest for fungal community structure analysis and soil nutrient determination. The results showed that there were no differences in pH between the different treatments compared to S0. However, the mass ratios of total phosphorus, available phosphorus, and ammonium nitrogen increased. Compared to S0, the other straw return treatments significantly increased the fungal Chao1 index and ACE index. Straw treatments caused significant changes in fungal community structure. Regarding community composition, the relative abundances of Ascomycota and Sordariomycetes in soils with straw return increased by 8.11% to 25.31% and 21.63% to 39.23%, respectively, compared to S0, while the abundance of Hypocreales decreased by 44.92% to 48.25%. Redundancy analysis indicated that the fungal community was mainly influenced by total phosphorus, available phosphorus, and nitrate nitrogen. This study demonstrates that adding an appropriate amount of straw significantly increases the content of total phosphorus and available phosphorus in the soil. Straw return altered the fungal community structure in paddy soil, with RDA and correlation analysis showing that total phosphorus, available phosphorus, and nitrate nitrogen significantly affected the structure of the fungal community.