A control method of shifting gear in an automatic manual transmission to pass from a current gear to a successive gear; the automatic gear transmission comprises a gearbox provided with at least one primary shaft and at least one secondary shaft connected to driving wheels, and at least one clutch interposed between the primary shaft of the gearbox and a drive shaft of an engine; the control method comprises the steps of: determining, when the clutch is at least partially closed, a target torque that has to be transmitted through the clutch; determining, when the clutch is at least partially closed, a rotation speed target of the drive shaft of the engine; and determining a target engine torque of the engine according to the target torque that has to be transmitted through the clutch and according to the rotation speed target of the drive shaft of the engine.