Abstract: In order to explore the effect of sludge biochar on passivation and remediation of Cd-contaminated soil, pot experiments were conducted to simulate the Cd-contaminated soil, and the effect of biochar on pH, organic carbon, Cd content and its valence state, plant height, enrichment coefficient and biotransformation coefficient of Cd-contaminated soil were investigated. The experimental results showed that the biochar prepared at 800℃ had better repair effect than that prepared at 300℃, and the optimum dosage of biochar was 9.0 g/kg. The content of Cd in soil also increased to 7.9 mg/kg at 800℃, which was about 1.0 mg/kg higher than that under 300℃ pyrolysis. Sludge biochar significantly reduced the content of acid extractable and reduced Cd in soil, but increased the content of oxidized and residual Cd. When the pyrolysis temperature was 800℃, the Cd content of acid extractable and reduced state was reduced to 0.68 mg/kg and 0.45 mg/kg, respectively, and the Cd content of oxidation state and residue state was increased to 0.76 mg/kg and 1.72 mg/kg, respectively, thus reduced the content of bioavailable Cd in soil. In addition, biochar could reduce the bioconcentration and transformation coefficients of Cd.