Abstract: Aerobic composting is a key technology for the resource utilization of food waste, but it faces the challenge of low phosphorus recovery efficiency. This study constructed composting systems with different biochar addition ratios (5%, 10%, 15%) to analyze changes in physicochemical properties (temperature, pH, C/N ratio) and phosphorus speciation transformation using the Hedley phosphorus fractionation method. A self-designed composting reactor was employed with food waste, straw, and biochar as raw materials, under controlled initial conditions (60% moisture content, C/N ratio of 20-30), and the composting process was conducted continuously for 42 days. The results showed that compared to the control group, biochar-amended groups exhibited faster temperature rise, prolonged thermophilic phase, and higher peak composting temperature. Additionally, biochar addition reduced pH and electrical conductivity (EC) fluctuations during the maturation phase, maintaining them within a more optimal range. Furthermore, biochar accelerated the formation of humic acid-like substances and enhanced the humification rate of food waste. Regarding phosphorus transformation, biochar effectively increased the proportions of water-soluble inorganic phosphorus (H₂O-IP) and sodium bicarbonate-extractable inorganic phosphorus (NaHCO₃-IP) in the early composting stage, while significantly reducing the percentages of calcium/magnesium-bound phosphorus (HCl-IP) and residual phosphorus (Residual-P) in the later stage. This led to an increase in the ratios of available phosphorus and moderately labile phosphorus, thereby improving the biological availability of phosphorus in the compost product. Notably, the 10% biochar addition group (BC2) demonstrated a thermophilic phase extended to 10 days, a peak temperature of 64.6 ℃, a 257% increase in humification index compared to the initial value, an available phosphorus proportion of 29.7%, and reduced proportions of calcium/magnesium-bound phosphorus (34.8%) and residual phosphorus (9.5%). These findings highlight the potential of 10% biochar addition to accelerate composting processes and enhance phosphorus bioavailability, providing technical support for efficient phosphorus recovery in food waste composting systems.