The short pulse signal amplification of a microchannel plate was studied by the transmission line method. The distortion of a single pulse signal and the change of the gain of the channel were discussed in detail. When the signal saturation parameter was more than 1, charges extracted by the pulse front edge can decrease the gain of the pulse trailing edge, resulting in the decrease in the gain of the pulse back edge. In addition, the mutual interference between multiple pulses was analyzed. If the next pulse arrived before the electron charge extracted by the previous pulse was fully replenished, the amplification of the latter pulse would also be affected. The effect of signal frequency on the gain of a microchannel plate was studied. When the total charges of a single pulse were constant, increasing the signal frequency could decrease the gain of microchannel plate. And the effect of signal frequency on the gain of the microchannel was not significant for signals with a same average current. The correctness of the above analysis was verified by the irradiation experiment of pulse laser on the image intensifier.