<p>This study investigated the effects of phytic acid modified biochar (PBC) and original biochar (WBC) on the chemical speciation transformation of Pb, Zn and Cd in both acidic soil (GS) and alkaline soil (FS). The incubation experiment of biochars and soils were conducted up to 30 d. The results showed that the addition of biochars to soils can influence the properties of soils, such as soil pH, organic matter and morphology of iron and manganese oxides. WBC raised the pH of both soils by a maximum of 1.13, while PBC lowered the pH of both GS and FS by up to 1.97. Consequently, the availability and speciation distribution of heavy metals in soil with biochar changed. Both WBC and PBC can decrease the availability of Pb, Zn and Cd in GS, while only PBC700 (pyrolyzed at 700 ℃) decreased the availability of Pb in FS, maximally by 18.8%. Correlation analysis results indicated that soil pH and Fe/Mn oxides were the main factors affecting the speciation distribution of heavy metals in soils. Biochars decreased the availability of heavy metals in acidic soil mainly by increasing soil pH. Differently, biochar affected the speciation distribution of heavy metals in alkaline soil mainly by influencing the form of Fe/Mn oxides in soil. This study might provide a new strategy to remediate heavy metal contaminated soil.</p>