Abstract: Biochar is the common adsorbent with high quality, however the ash component in biochar could cover the functional groups on the surface and fill the pores, affecting the adsorption capacity on biochar. In order to investigate the effect of ash component in biochar on the adsorption capacity to Sr(Ⅱ), the biochar was obtained via the anaerobic pyrolysis method under different temperatures using the corn straw as the raw material. Then the biochar samples were treated with water, hydrofluoric acid and aqua reginis, and the Sr(Ⅱ) adsorption amounts on each sample were tested. Finally, the interaction mechanism of ash component on Sr(Ⅱ) adsorption to biochar was discussed via pH, elemental analysis, XRD, FTIR, SEM, etc. As shown in the results, the biochar sample obtained at 500 ℃ exhibits the perfect adsorption capacity. The adsorption capacity of biochar modified with HF increases by 15%. According to the results of adsorption kinetics experiments, all of the biochar samples are well described by pseudo-second-order kinetic model. According to the results of adsorption isotherms experiments, the adsorption data match the Langmuir model well. HF can decrease the contents of water-soluble cation and Si element, which can reduce the competitive adsorption with Sr(Ⅱ) and expose more adsorption sites, leading to an increase in the Sr(Ⅱ) adsorption capacity on biochar.