Combined batch sorption and in situ X-ray absorption fine structure (XAFS) provide direct assessment of the mechanisms for Pb(Ⅱ) sorption at the soil-water interface under different pH conditions. The XAFS data indicated that the inner-sphere Pb sorption complex with ionic character (Pb4(OH)4+4) dominated the Pb surface speciation, and the outer-sphere Pb sorption complex and the precipitation of calcium carbonate containing Pb(PbCaCO3) were also involved in the adsorption samples. Coordination number and radial distance of the first-shell Pb—O decreased from 0.172 7 to 0.166 6 nm and the percentage of inner-sphere complexes increased when the initial pH changed from 6.0 to 8.5, indicating that the mechanism of Pb(Ⅱ) sorption by the soil was pH-dependent.