A new cooling method for the main drive system of machine tool was present, especially for horizontal milling and boring machine.The machine main drive system was circulating cooled by a small hydraulic pump station, combined with aircooled cooling device. With rigorous design and calculation, the appropriate cooling device was chosen and the cooling system layout was reasonable arranged. Under the ambient temperature required by the machine,the main drive system cooling requirement was met, so the equipment could be stable operated. The cooling structure is compacted, clean and environmentally, improving the heat transfer efficiency, service life and spindle cutting accuracy.