A method for strengthening a housing comprises the following steps: providing a housing being made of colored glaze and having an initial temperature of about 480° C. to about 550° C.; and spraying the surface of the housing using a spray solution containing potassium nitrate, potassium silicate, diatomite, and water to create an exterior layer on the surface. The exterior layer contains K+ ions, and the concentration of the K+ ions gradually decreases from a maximum value in the area of the outside surface of the exterior layer to zero in the area of the inside of the housing.