The invention discloses a method for extracting scandium oxide from titanium slag chloride waste, belonging to the field of comprehensive utilization of vanadium titano-magnetite resources. The method comprises the following steps: a, adding water to titanium slag chloride waste, and leaching; b, adding a reducer to the supernate obtained in the step a, then adding humic acid, regulating the pH value, and filtering to obtain precipitate; c, adding a hydrochloric acid solution to perform acidolysis reaction, and then filtering to obtain a coarse scandium solution; d, respectively performing extraction, washing and back extraction on the coarse scandium solution by taking (2-ethylhexyl)-2-ethylhexyl phosphonate as an extractant, the hydrochloric acid solution as a washing agent and a sodium hydroxide solution as a back extractant, thus obtaining a pure scandium solution; and e, adding oxalic acid to perform scandium precipitation, and calcining to obtain scandium oxide, wherein the grade of the obtained scandium oxide is about 95%. The method disclosed by the invention is high in product quality and simple in process, reasonably utilizes scandium resources in the titanium slag chloride waste, and has favorable economic benefits and social benefits.