The invention discloses a method for quickly stabilizing the rotating speed used after load shedding of a steam turbine generator unit. By the adoption of the method, under the condition that the steam inlet amount of an intermediate pressure cylinder is insufficient after load shedding of the unit is completed, the steam inlet flow of a high pressure cylinder can be adjusted automatically so that the unit can be kept nearby a rated rotating speed, and the working pressure and working amount of operators at the steam turbine side are greatly decreased; and meanwhile, the unit can achieve grid connection as quickly as possible, unit safety is facilitated, the economic efficiency is guaranteed, and the defects in the prior art can be overcome.