The invention relates to a novel planar Gunn diode and a preparation method thereof. The novel planar Gunn diode comprises an insulating substrate and a channel layer which are arranged from bottom to top in sequence, as well as a first electrode part and a second electrode part which are arranged on the channel layer, wherein at least one of the first electrode part, the second electrode part and the channel formed by the first electrode part and the second electrode part is integrated; the electrode edge of the first electrode part and the electrode edge of the second electrode part are not parallel; at least two intervals exist between the electrode edge of the first electrode part and the electrode edge of the second electrode part, so that signals of multiple frequencies can be generated at the same time, on one hand, the novel planar Gunn diode can be applied to the fields of multifrequency radar, color terahertz imaging and the like requiring signal sources of multiple frequencies simultaneously, and on the other hand, by using the own frequency mixing effect of the novel planar Gunn diode, a high-frequency signal, of which the frequency is the sum of such signal frequencies can be generated, so that the transmitting frequency of a device is increased greatly.