The utility model discloses an efficient water-jacket-free crystallizer suitable for a small square billet high-casting-speed continuous casting machine. The efficient water-jacket-free crystallizer comprises an upper flange, a top plate, a water tank partition plate, a water-jacket-free copper pipe, a shell, a lower flange, a bottom plate and crystallizer foot rollers. An up-down through circularhole is machined in a thick-wall copper pipe for producing a large-section casting blank to form a cooling water channel, a rectangular slotted hole is machined in the outer portion of a thin-wall copper pipe for producing a small-section casting blank, and then the thin-wall copper pipe is wrapped with a non-metal material to form the cooling water channel. The upper portion of the water-jacket-free copper pipe is fixed to the top plate through an upper flange, and the bottom of the water-jacket-free copper pipe is sealed through a lower flange and a sealing ring arranged on the bottom plate. During use, the water-jacket-free copper pipe is cooled more uniformly, and the yield of a casting machine is increased; the copper pipe can be quickly replaced on line, so that the spare part quantity of the crystallizer assembly is greatly reduced; and during electromagnetic stirring, the central magnetic induction intensity is higher than that of a conventional crystallizer, and the energy consumption is lower under the same stirring intensity.