The energy resolution refers to the minimum energy interval that a scintillation detector can measure for two incident particles of different energies. The single-energy particle with energy E is incident in the scintillator and absorbed completely, and transforms to an excited light of the scintillator, transmits, and then is detected by a photodetector and processed by the circuit so that the output pulse is a statistical distribution. The ratio of the full width at half maximum(FWHM) to the peak position of the distribution spectrum is defined as the energy resolution of the scintillation detector. The intrinsic energy resolution of the scintillator can be obtained by subtracting the contribution of the photodetector. In high-energy physics experiments, the standard deviation σ after Gaussian fitting of pulse distribution spectrum is used as energy resolution, but its physical meaning is different.