This invention provides a method for forming multilayer coating film excelling in smoothness and distinctness of image, by 3-coat-1-bake system in which a step of applying onto a coating object a water-based intermediate paint (X) to form an intermediate coating film; a step of adjusting the solid content of the intermediate coating film to 70-100 mass %; a step of applying onto the intermediate coating film a water-based base coating paint (Y) containing 30-55 mass parts of alcoholic solvent having a boiling point of 170-250° C., to form a base coating film; a step of adjusting the solid content of the base coating film to 70-100 mass %; a step of applying a clear paint (Z) comprising 40-60 mass parts of carboxyl-containing compound and 60-40 mass parts of polyepoxide onto the base coating film to form a clear coating film; and heating the intermediate coating film, base coating film and clear coating film at 100-120° C. for 3-10 minutes and thereafter further heating them at 130-160° C. for 10-30 minutes; are successively carried out.