Corn and rice stalks were used as raw materials to prepare biochar（CS, RS） at 500℃ under oxygenlimited conditions. The two biochar types（CS and RS） were functionalized with polyethyleneimine（PEI） to obtain another two straw-based biochars（PC and PR）. The morphology, structure and surface characteristics of the four types of biochar were characterized by field emission scanning electron microscope, automatic specific surface and porosity analyzer, Fourier transform infrared spectrometer and X-ray powder diffractometer. The results showed that the surfaces of the straw biochars after functionalization（PC and PR） became smoother and the specific surface area increased significantly, the absorption peaks of oxygen-containing functional groups were enhanced, and an aromatic structure emerged. The adsorption experiments indicated that the equilibrium adsorption capacity of Pb²⁺ by the biochar of CS, PC, RS, and PR were 84.6 mg·g^-1, 93.1 mg·g^-1, 88.6 mg·g^-1 and 98.2 mg·g^-1, respectively. Both the Langmuir（R²≥0.963） and Freundlich（R²≥0.955） models showed good correlations to the adsorption of Pb²⁺.