Abstract: Water washing could remove the pyrolysis by-products attached to the surface of biochar when the biochar properties remained unchanged, which would ensure the removal ability of heavy metal. The adsorption and desorption characteristics of Cd²⁺ and Pb²⁺ and the soluble salt contents by different biochar types derived from wheat and rice straw were compared in this study. Results showed that the adsorption processes of Cd²⁺ and Pb²⁺ by biochar were better fitted a pseudo second order kinetic model and a Langmuir equation. The maximum adsorption capacities of biochar from wheat straw on Cd²⁺ and Pb²⁺ were 12.82 mg g⁻¹ and 9.91 mg g⁻¹, which were 1.31-1.76 and 1.06-1.53 times than that from rice straw. Removing soluble salt with water washing decreased the adsorption capacities of Cd²⁺ and Pb²⁺ by biochar. After water washing, the maximum adsorption capacities of biochar derived from wheat and rice straw on Cd²⁺ decreased by 42.36% and 60.13%, and the sorption capacities on Pb²⁺ decreased by 29.47% and 62.72%. However, the desorption rates of Cd²⁺ and Pb²⁺ were higher by biochar from wheat straw than that from rice straw. The maximum desorption rates of the un-washed biochar on Cd²⁺ and Pb²⁺ were 1.84%-13.05% and 1.57%-11.82%, while those of the washed biochar were 7.88%-20.19% and 6.34%-16.94%, respectively. Therefore, water soluble salts in biochar play an important role in the adsorption/desorption of Cd²⁺ and Pb²⁺. These results would provide technical support to prepare biomass materials for remediation of heavy metal contaminated soil.