In order to master the false alarm laws of dual frequency electromagnetic radiation in band to radar, the stepped frequency continuous wave radar was taken as the research object, based on the theoretical analysis and effect test, the level change law, waveform characteristics and location law of false alarm target were studied. Results show that:under the effect of dual frequency electromagnetic radiation in the band, the tested radar can generate at most two “hill type” false alarm targets with random positions without considering intermodulation interference, and the distance difference is related to the frequency difference of dual frequency interference. The two components of the dual frequency interference signal suppress each other, that is, if the intensity of one component is constant, with the enhancement of another component, the level of the false alarm target formed by the former decreases slowly and the final deceleration is basically constant, while the level of the false alarm target formed by the latter increases gradually until the level is constant. If the strength of the two components of the dual frequency interference signal increases in the same proportion, the levels of both two false alarm targets rise approximately linearly at the initial stage, and then the growth rate gradually decreases to zero.