The invention relates to a method for extracting scandium oxide from tungsten steel slag. The method includes the steps: firstly, using a fine ball mill to crush the steel slag prior to performing main processes of inorganic acid leaching, organic solvent extraction, oxalate precipitation and the like, and enabling scandium in the tungsten steel slag to leach by the aid of sulfuric acid; secondly, allowing leaching liquor to stand to precipitate titanyl sulfate, filtering and removing titanyl sulfate, diluting mother liquor by slag washing water, and using the diluted mother liquor as feed liquor 1 of the extracted scandium; thirdly, dissolving the filtered titanyl sulfate solids by the slag washing water, and using filtrate with insoluble impurities as feed liquor 2 of the extracted scandium; fourthly, extracting the feed liquor 1 and the feed liquor 2, performing back extraction for a loaded organic phase by NaoH solution, and using sulfuric acid to dissolve hydroxide obtained after back extraction; fifthly, removing titanium by water, subjecting scandium-rich liquor with the titanium removed to secondary extraction according to conditions, washing the loaded organic phase by sulfuric acid solution containing Nacl and H2O2, then using NaoH solution for back extraction, and performing filtering, ignition and hydrochloric acid dissolving for scandium hydroxide obtained after back extraction; and finally, precipitating scandium oxalate from oxalate, and then converting the scandium oxalate to the scandium oxide by means of ignition.