Abstract: When the waveform of a radiation pulse is measured, a large number of radiation particles interact with the detector simultaneously. The output current waveform is proportional to the waveform of the radiation pulse. The statistical fluctuation phenomenon will appear when the radiation source is relatively weak or the sensitivity of the detector is low. In this paper, the fluctuation phenomenon are considered and mathematical expressions for fluctuation are given. We have also discussed the uncertainty due to statistical fluctuation of various pulse parameters measured, such as amplitude, width, time interval and other special parameters.