Nowadays, much attention in electronic warfare is paid to the Specific Emitter Identification (SEI), which seems to be one of the most difficult subjects in the field. The principal function of the SEI is recognizing the different radar devices of the same type. In most cases, classical methods of identification could not be enough to realize the task. The main unique characteristics of a modern radar emitter are hidden in the structures of the time-domain waveforms, especially the pulse envelope and instantaneous frequency, which are used as the fingerprint features in this paper. In order to measure the distinctions among different radar emitters of the same type, the frechet distance which provides an effective way to calculate the distance between curves, the pulse envelopes or instantaneous frequencies, is chosen to achieve the SEI. The basic theory of the frechet distance is described and the experimental results are presented in the paper.