The present invention is a first step of detecting a stroke of the casting-related information including the casting speed, the sliding gate tundish in a continuous casting process; A second step of the stroke of the tundish slide gate calculates the molten steel level, and calculate the distance of the bottom of descent redeul long nozzle; When the comparing the fall distance and the reference value set in advance, respectively, and the ladle exchange, is greater than the reference value by controlling the descent of the future according to the comparison result and then proceeds to the first step, the ladle descent is less than the reference value and a third step of stopping the injection of molten steel in the tundish to the nozzle openings Long; A fourth step of detecting a stroke of the casting-related information including the casting speed, the sliding gate tundish in a continuous casting process; The stroke of the tundish slide gate calculates the molten steel level, and a fifth step of calculating the rising and falling distance of the bottom redeul long nozzle, respectively; Said comparing the fall distance and the reference value set in advance, respectively, during the molten steel injection, is greater than the reference value and then controlling the fall and rise of the future according to the comparison result and proceeds to step 4, if smaller than the reference value and a; ladle sixth lowering and stopping the rise. Ladle (Ladle), tundish (Tundish), slag (Slag), net steel, immersion depth, mold (Mold), Sliding gates (Sliding Gate)