This disclosure provides a method for treating an etching waste liquid from an etching process of indium tin oxide comprising hydrochloric acid, acetic acid, tin ions, indium ions and water, comprising the steps of: distilling the etching waste liquid to obtain a distillate comprising hydrochloric acid and acetic acid and a post-distillation liquid comprising tin ions and indium ions; generating a precipitate by reacting tin ions in the post-distillation liquid with sulfide ions to remove tin ions from the solution so as to obtain a post-precipitation solution containing indium ions; and electrolyzing the post-precipitation solution to obtain crude indium.