The relationship of the gain logarithm and voltage of microchannel plate is linear in theory. In order to be closer to the actual situation, according to the known function between the voltage and logarithmic gain of microchannel plate, a set of linear data points added random numbers were selected, and the new relationship of the voltage and logarithmic gain was obtained which can be used to restore the target distance information. The analysis results of imaging accuracy show that the imaging accuracy is related to the system’s signal noise ratio and gain modulation function, the higher signal noise ratio is, the higher the distance accuracy is. The relationship between the gain and the voltage of microchannel plate was measured. The echo images in different voltages conditions were obtained by illuminating the same target at the same distance, the gray value ratio of the echo images under different voltages was used to get the ratio of relative gain. Respectively under the condition of constant gain and modulation gain, the target which was 60 m far from the imaging system was imaged. By using the gain curve, the obtained images were processed and the distance information of target accurately was restored, the distance accuracy could reach decimeter magnitude.