This paper analyzes the statistical fluctuation of scintillation detectors in the field of low intensity gamma pulse rays. It is found that the statistical fluctuation of scintillation detectors is affected not only by intensity of incident gamma pulse rays

timing distribution

spatial distribution and energy distribution

but also by interaction between gamma rays and detectors

energy deposition

emission and transportation of fluorescence photons

interactions between fluorescence photons and photocathode

and between photoelectrons and dynodes. The formula on statistical fluctuation of scintillation detectors is deduced. The statistical errors of three types scintillation detectors composed of different scintillators and photomultiplier tube 9815B under the lowest measurement limit of gamma pulse rays are estimated.