A practical engineering method is presented that can test the gapless harmonic analysis using power quality analyzers.According to an analysis of the difference in the FFT frequency components between the gapless and gap measurements，a test based on the aggregation algorithm is designed.After considering the limited number of equipments and the impact of various factors of the equipment under test（EUT），the specific fluctuating harmonic is selected as the test signal.Then the EUTs harmonic measurement times in three seconds can be detected by the duration of the waves pulse that can be sampled.In addition，a calibration system is designed by LabVIEW programming.The computer controls the standard power source to emit the test signals required.The effectiveness of the method for calibration is verified and the accuracy of the system is proved.