Abstract: Spreading through in the interstellar space,pulsar signals, due to the existence of the interstellar medium, would be observed dispersively, therefore we need to remove dispersion of the received pulsar signals for obtaining the original pulsar signals. The current de-dispersion methods are mainly divided into two types, coherent de-dispersion and incoherent de-dispersion. Relatively speaking, the former is able to eliminate dispersion completely, which has simpler algorithm, and preserves the time resolution of the original signal. Although it has a larger amount of calculation, rapid progress of computer technology can solve such problem. In order to accurately understand the difference between the two methods of de-dispersion, this paper, adopting the method of coherence coefficient, quantitatively compares the effects of coherent de-dispersion and incoherent de-dispersion:below a certain frequency, the former is better than the latter in obtaining the de-dispersion effects. Meanwhile, the observed frequency of the two de-dispersion methods at the same effect is determined.