The invention discloses a controlled cooling method for a plate blank electroslag furnace, which adjusts the flow of cooling water based on the thicknesses of the narrow side and the broad side of a crystallizer. By adopting the method disclosed by the invention, the internal quality of a steel ingot (electroslag ingot) meets the requirements, and the surface quality of the steel ingot is improved. Proven by experiments, by the cooling method disclosed by the invention, the overall yield of blank-electroslag ingots is 98.18%, the yield of blank-electroslag ingot-material is 81.04% which is improved by about 10% as compared with ordinary steel ingots, wherein the yield of steel plates produced by a 640 type crystallizer is 83.76%, the yield of steel plates produced by a 760 type crystallizer is 78.77%, the yield of steel plates produced by a 960 type crystallizer is 74.58%, and the percent of pass in flaw detection is 100%.