Abstract: It is very important to analyze the statistic character of detector signal of container inspection system and further to choose suitable image scanning parameter. In the paper, by introducing the concept of equivalent statistical time, the detector signal could be analyzed easily and clearly. Also the statistical fluctuation character of detector signal under different scanning conditions is described by examples, and we can get some rules of decreasing the detector signal statistic noise by the average method of a certain times of measurement. This work can provide some directions in theory.