The invention discloses alkali modified biochar and a preparation method thereof, and a method for removing emerging pollutants in sewage by using the modified biochar. The method comprises the following steps: preparing initial biochar by using a pyrolysis carbonization method, dipping the initial biochar in an alkaline solution, oscillating and fully contacting, washing with ultrapure water until the pH value is neutral, and carrying out suction filtration and drying to prepare the alkali modified biochar. Compared with the initial biochar, the alkali modified biochar prepared by the invention has larger specific surface area and stronger hydrophobicity, and has higher adsorption capacity and better removal effect on emerging pollutants bisphenol A and antibiotics (tetracycline TC, ofloxacin OFL and the like). Meanwhile, pollutants adsorbed on the alkali modified biochar are not easy to desorb, so that secondary pollution is avoided. In conclusion, emerging pollutants in sewage can be effectively removed, meanwhile, secondary pollution of the alkali-modified biochar after adsorption is little, and the method has the advantages of being easy to operate, efficient, environmentally friendly, capable of saving cost and the like.