The invention discloses a forging method for forged steel supporting rolls used for a rolling mill of large-scale wide thick plates. A double-vacuum steel ingot is adopted to manufacture the forged steel supporting rolls, wherein the weight of the double vacuum steel ingot is no less than 250 tons, an average diameter of an ingot body is no less than phi 3300mm, and the height of the ingot body is no less than 4000mm. The forging method comprises a first step of prepulling; a second step of upsetting: carrying out heat preservation on the steel ingot for 30-50 hours with the temperature of 1200-1250 DEG C, and then carrying out upsetting on the steel ingot on an open die forging hydraulic machine through adoption of an upsetting plate and a forging method of wide anvil forcing; a third step of carrying out drawing out on the steel ingot through adoption of a forge operation machine and a tilting gear and through the forging method of the wide anvil forcing; and a fourth step of distributing materials until completing is achieved according to a forging drawing. In the forging process, an as-cast structure of the steel ingot can be smashed, internal gaps can be forged and combined, metal inclusions and out-phase particles are dispersed, so that a workpiece can obtain a fine and even recrystallized grain structure and obtain a reasonable fiber distribution trend, and requirements on structure property of the support rolls by the support rolls of large-scale wide thick plates are met.