The invention discloses a desizing process of high-temperature discharge of a gray fabric. The process comprises the following steps: (1) filling a dye vat with a proper amount of water, heating to 50 DEG C, carrying out heat preservation for a period of time, and further adding the gray fabric; (2) then adding auxiliaries into the dye vat; (3) then raising the temperature of an aqueous solution to 130-135 DEG C and carrying out heat preservation for 20-30 minutes; (4) after heat preservation, conveying high-temperature sewage in the dye vat to a heat exchanger, and meanwhile, further injecting clean water into the heat exchanger, wherein the high-temperature sewage is cooled after heat exchange and the cooled high-temperature sewage is directly discharged, the clean water after heat exchanger is heated, and the heated clean water is conveyed to the dye vat to wash the gray fabric in the dye vat; (5) drying the gray fabric after washing. According to the desizing process disclosed by the invention, the high-temperature sewage in the dye vat can be directly discharged through the heat exchanger, so that the time of dyeing and printing production process is shortened, the cost is lowered, the washing effect of the gray fabric in the dye vat is further improved, and the electric energy and the water energy are saved.