Abstract: The method of sequential continuous-casting of the different grades of steel according to the present invention comprises the steps of: stopping the pouring of a first grade of molten steel into a mold; immersing a cooling material consisting of a steel structure slightly smaller than the inner cross-sectional area of the mold by way of guiding jigs fastened to said cooling material; forming a solidified phase around said cooling material; and merging said solidified phase in a solidified shell developed from the wall of the mold to form a solidified layer shutting the upper portion off the lower portion of the first grade of molten steel.