In this paper, three evaluation methods about the on-off ratio of pulse waves are introduced, they are the direct pulse width measurement method, the amplitude statistical method, and the average measurement method. The error sources are discussed, including the amplitude measuring error, the effect of the range of the mode of the density distribution method, and some others. The evaluation course of the uncertainty is presented. Combining with a group of experimental results, both the on-off ratio of pulse waves and its uncertainty are given out.