For the two pairs of pulses separated by time delay, the transmission characteristics between the pulses will be affected according to the changes of phase and delay, and the interference phenomenon will occur in the pulse overlap area due to the influence of cross-phase modulation. The article proposes to observe the transmission characteristics of pulse pairs in a dispersion-decreasing fiber loop mirror. The research results show that according to the changes in phase and delay between the pulse pairs, the time domain characteristics and chirp characteristics of the pulse pairs can be observed, and the transmission characteristics of the pulse pairs under different conditions are analyzed.