In this paper

the influence of the phase synchronization of the fundamental wave current and harmonic current on the noise value in noise measurement of the capacitor unit used in AC filter for HVDC transmission project is discussed

and the causes of the fluctuation of the noise value are tested and analyzed. Meanwhile

the relationship between the magnitude of the loaded current and the noise value and the influence of the noise sampling time on the test results are compared. The results of the study have some guidance and reference significance to the AC filter capacitor unit noise test.