The invention relates to a shifting method for an AMT (Automated Mechanical Transmission) automatic gearbox. The shifting method comprises the following steps A, during a driving process of a vehicle, judging whether shifting to other advancing gears or not according to a vehicle driving state parameter and an operation signal, if yes, executing step B, and if not, repeating step A; B, determining a target gear; C, calculating a target rotating speed of an engine according to a rate of the present vehicle speed to the gear speed of the target gear; D, judging whether the target rotating speed of the engine is greater than or equal to an idle speed or not, and if yes, executing steps E-G; E, maintaining the present rotating speed and using a shifting motor for retreating a present gear synchronizer to a neutral gear; F, controlling a gear selecting motor to act, and controlling the rotating speed of the engine to the target rotating speed of the engine when the gear selecting motor moves to the target gear position; G, controlling the gear selecting motor to act, shifting a target gear synchronizer to the target gear, cancelling the control on the rotating speed of the engine and finishing the gear shifting.