The invention belongs to the technical field of microwave and millimeter wave testing, relates to the reflectivity testing of wave absorptive materials of microwave and millimeter wave, and provides a testing device that measures the reflectivity of the wave absorptive materials according to an arc method. Compared with existing reflectivity testing devices of the wave absorptive materials with arc methods, the invention provides an arc rail that consists of a first ally arm (7) shaped like a character '7' and a second ally arm (8) and can rotate around a rotating shaft of an electric rotating motor (12). When utilized in the reflectivity measurement of different incident angles, the testing device has ultra-convenient angle control and fixed radiuses of the ally arms, and can reduce the testing error that is caused by radius change. After adopting the structure that is shaped like the character '7', the testing device has reduced volume, and consequently can effectively reduce the disperse emission that is caused by an antenna fixing frame, raises measuring precision, and is convenient for loading, unloading, transportation and storage.