The invention discloses a gear steel 20CrMnTiH isothermal normalizing treatment method, and belongs to the field of material thermal treatment. The gear steel 20CrMnTiH isothermal normalizing treatment method comprises the steps: adopting a warm-air district cooling technology after austenitizing heating: in district I, the warm air temperature is 50 to 55 DEG C, the air speed is controlled to be 8 to 12 m/s, and the air cooling time of parts is controlled to be 2 to 3 minutes; in district II, the air temperature is 55 to 60 DEG C, the air speed is 5 to 8 m/s, and the air cooling time of parts is controlled to be 3 to 4 minutes; regulating an isothermal normalizing furnace to be in two-stage control: first stage, the temperature is controlled to be 550 to 570 DEG C, and the heat preservation time is 1 to 1.5 hours; second stage, the temperature is controlled to be 570 to 600 DEG C, and the isothermal control time is 1 to 1.5 hours; after isothermal normalizing, entering an air cooling chamber, controlling the air temperature to be 30 to 40 DEG C and the air speed to be 5 to 8 m/s, and carrying out air cooling after cooling to 200 to 250 DEG C. The hardness of gear blank treated by the technology can be up to 165 to 180 HB, the pearlite interlamellar spacing is controlled to be 0.18 to 0.24 mu m, the grade of a banded structure is controlled to be 1 to 1.5, the cutting performance is good, deformation after quenching can be stably controlled, and the reject ratio is basically zero.