In this study, biochar were produced from coconut shell and peanut shell, and then modified with 14% H₃PO₄ and 1.0 mol/L NaOH-30% H₂O₂, respectively. The changes of physicochemical properties of biochar before and after modification and the sorption mechanism of diethyl phthalate (DEP) were studied. The results showed that the aromatization degree and the content of oxygen-containing functional groups of modified biochar increased, the specific surface area (SA) increased except C300N (the 300℃-coconut shell biochar modified by NaOH-H₂O₂). P800N (the 800℃-peanut shell biochar modified by NaOH-H₂O₂) had the highest sorption affinity for DEP because of the largest SA (584.22 m²/g). The sorption affinity of DEP by the NaOH-H₂O₂ modified biochar was stronger because of the higher organic carbon partition coefficient K_oc (C_e=0.1S_w) value. The π-π EDA interaction played an important role in the sorption of DEP by all biochar, while the pore-filling effect regulated the sorption of DEP by the original biochar, NaOH-H₂O₂ modified biochar and H₃PO₄ modified 800℃-biochar. The water clusters formed by hydrogen bonding inhibited the sorption of DEP by the 300℃- and 500℃-biochar modified by H₃PO₄ compared with the original biochar. In addition, the hydrogen bonding was helpful to enhance the sorption affinity of low-temperature (300℃) biochar for DEP.