The invention provides a treatment method for RGB (Red, Green and Blue) waste liquid and depainted waste sulfuric acid. The method comprises the following steps: mixing the RGB waste liquid with the depainted waste sulfuric acid, controlling a pH value of a reaction endpoint, and cooling and filtering a mixed solution to obtain a potassium sulfate crystal A and a mother solution; concentrating the mother solution to obtain a potassium sulfate crystal B; adding water into the potassium sulfate crystal A and the potassium sulfate crystal B for dissolving, then adding an adsorbent for adsorbing impurities, and filtering to obtain a potassium sulfate solution and a waste adsorbent; and concentrating and recrystallizing the potassium sulfate solution to obtain potassium sulfate. The treatment method for the depainted waste sulfuric acid and the RGB waste liquid, disclosed by the invention, has the advantages of low treatment cost, simple operation, wide application range as well as diversified and high added-value recycled products; and relatively-high economic benefits can be generated and relatively-high environmental benefits are obtained.