The sewage sludge-derived biochar was prepared from sewage sludge and then modified by nitric acid to obtain acidified sewage sludge-derived biochar (SSB-AO). The effects of SSB-AO dosage, initial pH of solution, coexisting ions concentrations, adsorption time, initial concentration of U(Ⅵ) and adsorption temperature on the removal of U(Ⅵ) by SSB-AO were investigated. The removal mechanism was analyzed by SEM-EDS, FTIR and XPS. The results show that the adsorption of U(Ⅵ) by SSB-AO is in accordance with the quasi second-order kinetic model, which indicate that the adsorption is mainly chemical adsorption process. The isotherm adsorption process is according with Langmuir model. Under the conditions of 30 ℃, 0.01 mol/L NaNO3, adsorption time of 300 min，initial pH of 6, initial uranium concentrations of 10 to 100 mg/L and dosage of 0.6 g/L, the theoretical maximum adsorption capacity is 80.34 mg/g. The adsorption efficiency of SSB-AO is more than 88% after five adsorption desorption tests, which shows that SSB-AO has nice circulation ability. The mechanism of U(Ⅵ) removal by SSB-AO include inner surface complexation, electrostatic adsorption and ion exchange. This study shows that sewage sludge-derived biochar, after modification by nitric acid, can effectively improve U(Ⅵ) adsorption capacity, which provides a reference for U(Ⅵ) containing wastewater treatment.