A set of measurement system of scintillator decay time constant is built up based on the principle of delayed coincidence method of single photon technology. Three pieces scintillation crystals of Ce:LYSO and Ce∶LuAG scintillators were selected to measure the decay time. The single exponential fitting of the decay time constant curve obtained from the measurement is carried out. The calculated decay time constant average of Ce∶ LYSO is 43.85 ns; the decay time constant average of Ce∶LuAG is 56.02 ns. The test results of the device are basically consistent with those of other measurement methods at home and abroad.