The invention provides an external protection of a grinder. The main structure of the external protection comprises a protective cover body, a glass window and a lower hoarding, wherein the protective cover body is fixedly installed on a grinder base oil-receiving tray, the glass window is installed on the protective cover body, and the lower hoarding is installed on the grinder base oil-receiving tray and connected with the lower end of the protective cover body. The protective cover body on the position of a machining station of the grinder is designed with an arc-shaped revolving door, the upper portion of the arc-shaped revolving door is designed with a top protective cover in a closed mode, and the top protective cover is lower than and parallel to the top of the protective cover body; and the top protective cover is connected with the top of the protective cover body through a rotating mechanism, a roller mechanism is installed at the bottom of the arc-shaped revolving door, and an arc-shaped track used for supplying the roller mechanism to slide is installed above the oil-receiving tray corresponding to the arc-shaped revolving door. The machine-tool external protection of the structure obviously enlarges the opening space of a machine tool, and positioning, picking and placing of a workpiece and maintenance and cleaning of the machine tool are convenient.