The invention relates to a fine-grain roll-forming method for a large annular piece made of high alloy steel. The method is characterized by mainly comprising the following steps of: (1) blanking; (2) heating, and preserving the temperature, namely heating a material section from room temperature to a set temperature line Accm with high plasticity and low deformation resistance in a heating furnace, and preserving the temperature for more than 2 hours; (3) forging, namely rounding and lengthening the material section sequentially, upsetting the material section for the first time, and lengthening; (4) returning into the furnace, heating, and preserving the temperature, namely returning the lengthened forged bar into the furnace, heating to the temperature which is 50 DEG C below the Accm line, and preserving the temperature for 0.5 to 1 hour; (5) making a blank, namely performing upsetting, punching, slug-stamping and end-face flattening on the hot-forged bar, and thus obtaining an annular piece blank; and (6) roll-forming, namely putting the obtained annular piece blank on an annular rolling machine for rolling, and controlling the rolling process according to three stages, namely pre-rolling, rolling and determining the diameter of a whole circle on the basis of the temperature and the rolling speed. The method has the characteristics of high production efficiency, low production cost and high product quality.