The invention relates to a method for recycling waste diluted sulfuric acid from steel washing, belonging to the filed of the metal post-treatment. According to the technical scheme, the method for recycling the waste diluted sulfuric acid from steel washing comprises the following steps: (1) preliminarily precipitating and filtering the waste diluted sulfuric acid from steel washing in such a way of leading the waste diluted sulfuric acid from steel washing into a primary precipitating pond, cooling the waste diluted sulfuric acid to the room temperature, and leading the waste diluted sulfuric acid into a secondary precipitating pond; (2) secondarily precipitating the waste diluted sulfuric acid in such a way of adding and stirring evenly calcium hypochlorite to the waste diluted sulfuric acid in a secondary precipitating pond, and removing impurities; (3) cooling and crystallizing the waste diluted sulfuric acid in a coolling crystallizer; and (4) leading the diluted sulfuric acid mother solution for separating the ferrous sulphate hydrated crystal to an acid pickling solution preparing container to prepare acid pickling solution meeting the process requirement. The method for recycling the waste diluted sulfuric acid from steel washing can greatly reduce the use amount of the acid of the acid pickling enterprises and ensure that no waste diluted sulfuric acid is discharged and the waste diluted sulfuric acid is generated into the useful by-product, thereby achieving the purpose of protecting the environment, saving the resource and reducing the production cost.