Abstract: A low background HPGe gamma ray spectometer is constructed, whencalibrate its detection efficiencies, gamma ray standard (or reference) sourceswhich are prepared by several laboratories were used. It is found that althoughthe efficiencies are repeatable for each set, the deviations at some calibrationpoints are much larger than total uncertainties involved. The factor may be thatsome sources passed their time of efficacy (1--2 a) but not recalibrated atregular intervals. The results observed implies that in gamma ray spectra analysesattention should be paid to the quality assurance in the processes of preparingand calibrating standard sources and in recalibrating them at regular intervals.