The invention belongs to the field of wastewater treatment, and discloses a method for removing As (III) in wastewater by enhanced coagulation, which mainly comprises the following steps: (1) adding acertain amount of calcium peroxide into As (III) containing wastewater, and stirring; and (2) adding an inorganic coagulant to carry out coagulation treatment. According to the method, in the treatment process, on one hand, calcium peroxide plays a role of an oxidizing agent; As (III) is converted into As (V), and on the other hand, the pH environment in the water body solution is improved by utilizing slow hydrolysis of calcium peroxide in the water body solution, so that the pH in the coagulating sedimentation process is maintained at a slightly alkaline level beneficial to coagulating sedimentation, the coagulating efficiency is improved, and meanwhile, the efficient coagulating efficiency and oxidation efficiency are realized. The method is simple to operate and low in cost, does notneed additional equipment investment, and can be widely applied to advanced treatment of arsenic-containing industrial wastewater and treatment of arsenic-polluted underground water or drinking water.