The invention provides a cross beam grinding machine of a machine tool, and relates to the technical field of grinding machines. The machine involves the machine tool, wherein a sliding rail is fixedly arranged at the top of the machine tool, a bearing plate is slidably connected at the top of the sliding rail, an air cylinder is fixedly arranged at the top of the bearing plate, a workbench is fixedly arranged at the end, away from the bearing plate, of the air cylinder, an impurity removing structure is fixedly arranged at the top of the machine tool, and a machining structure is fixedly arranged at the position, on the top of the impurity removing structure, of the top of the machine tool; and the impurity removing structure comprises a sealing cover, the inside of the machine tool is slidably connected with the sealing cover, and the inside of the sealing cover is fixedly provided with a motor. According to the grinding machine, a magnet moves along the outer surface of a threaded rod to attract waste materials, particularly waste materials at the four corners of a rectangular groove, so that the cleaning quality is higher, and the cleaning efficiency is improved; and meanwhile,the magnet further cleans the outer surface of the magnet through a cleaning brush, and the waste materials fall into a collecting groove, so that the effect of quick cleaning is achieved, convenience is provided for later cleaning, and the labor intensity of cleaning personnel is reduced.