A method and device for strengthening the laser shock of a hidden surface includes establishing a continuous laser shock strengthening track and process after acquiring the information about the whole hidden surface. A control system adjusts the movement and rotation of a total reflection mirror which is arranged in a workpiece according to the signal from signal collecting cards for making a reflected laser beam act on a region to be machined of the hidden surface at an appropriate incidence angle. The method can realize the surface strengthening treatment of the hidden surface of the workpiece, significantly improve the mechanical performance of the workpiece and increase the fatigue life thereof, which is applicable to the surface strengthening of the workpiece with the hidden surface.