The invention relates to a device for protecting a laser beam expanding lens. The device is installed at an incident end of the beam expanding lens and includes a window lens barrel, a window lens base, and a window lens. One end of the window lens barrel is an installation end for fixed connection with the beam expanding lens, and the other end is an interface end for external connection. A light through hole is arranged in the interface end. A lens base installation hole is arranged in the installation end. The light through hole communicates with the lens base installation hole. The centers of the lens base installation hole and the light through hole are eccentrically arranged. The window lens base is installed in the window lens base installation hole. The window lens is installed on the window lens base. The window lens base can be rotatable in the window lens barrel. Compared with the device in the prior art, the device of the invention has a simple and compact integral structure, is easy to adjust, and does not influence the usage and adjustment of the beam expanding lens. The window lens base can make the window lens recycle repeatedly through rotation. The service life is prolonged, and the cost is reduced.