Heavy metal pollution of soil and water has seriously threatened human life and health, and Pb2+ is one of the most difficult heavy metals to deal with because of its strong toxicity, difficult degradation and easy enrichment. Corn straw was used as raw material to prepare hydrochar and pyrochar at different temperatures (280℃ and 320℃), respectively. The structural differences of the two kinds of biochar were compared and analyzed, and based on this, Pb2+ adsorption mechanism of hydrochar and pyrochar from straw was studied by combining isothermal adsorption model and adsorption kinetic model. The results showed that the dehydrogenation effect of hydrochar was more significant, forming rich surface oxygen functional groups and disordered crystal structure with the increase of hydrothermal temperature. The porosity of hydrochar was firstly increased and then decreased, finally presenting a regular and dense appearance; however, the deoxidization effect of pyrochar was more remarkable, it had fewer surface oxygen functional groups, forming a more ordered crystal structure. The porosity of pyrochar continued to increase, showing a rough porous surface morphology. Adsorption equilibrium of straw hydrochar and pyrochar was reached at 4h and 10h respectively, and the theoretical equilibrium adsorption capacity was 214.16mg/g and 133.99mg/g; Pb2+ adsorption of straw pyrochar was in accordance with pseudo firstorder kinetic model and Freundlich isotherm adsorption model, indicating that the adsorption reaction was a multi molecular layer adsorption process; however, Pb2+ adsorption of straw hydrochar conformed to the pseudo secondorder kinetic model and Langmuir isotherm adsorption model, indicating that the adsorption reaction was a single molecular layer adsorption process. Combined with the structural characteristics of the two kinds of biochar, it was found that straw pyrochar mainly relied on the diffusion movement of Pb2+ within its pores to remove Pb2+ from water, and the existence of largescale mesopores was more conducive to Pb2+ to overcome the space barrier and enter the pores, however, the physical adsorption capacity was relatively weak and easy to desorb; in addition, complexation reaction was the main Pb2+ removal mechanism of straw hydrochar, in other words, the oxygencontaining functional groups exchanged with Pb2+ to form complexes, and chemical adsorption capacity was strong and not easy to desorb. 