A magnetically modified rice husk biochar was successfully prepared by a hydrothermal method and was subsequently used to remove phenanthrene(PHE)from water. The characteristics of removing phenanthrene from water by biochar before and after modification was analyzed. The influence of different factors on the adsorption effect of phenanthrene in water was discussed. SEM, FTIR, XRD and XPS were used to analyze the characteristics of original biochar(BC)and magnetic biochar(MBC)and the adsorption mechanisms. The results showed that the adsorption site, specific surface area and hydrophobic of biochar were significantly improved and enhanced after being modified. The adsorption to PHE by two biochars fitted well to pseudo-second-order kinetic and Langmuir models. The adsorption mechanism of the two biochars were mainly attributed to surface functional groups action and π-π conjugated reactions. The adsorption to PHE by MBC mainly occurred in the functional groups of C—O and Fe₃O₄, but that by BC was mainly in the functional groups of —OH, N—H, CC and C—O. Compared with other biochars, MBC has better application prospect in the removal of PHE from water.