The　digital　flicker　meter　often　calculated　the　frequencies　and　amplitudes　of　voltage　fluctuation　by　Fourier　transform　dealing　with　the　RMS　values　of　a　voltage　waveform　and　then　calculates　the　instantaneous　flicker　sensation　level　directly　by　checking　table.　Yet　the　above　process　was　usually　completed　by　numerical　calculation,　lack　of　accurate　analytical　expression.　So　dynamic　phasor　approach　was　adopted　to　calculate　the　analytical　expression　of　the　RMS　values　spectrum　of　power　frequency　voltage　modulated　by　single　frequency　sinusoidal　wave,　and　a　new　comparison　table　on　frequencies　and　corresponding　voltage　fluctuations　of　RMS,　which　make　instantaneous　flicker　sensation　level　to　be　one,　is　obtained.　The　analysis　show　that　the　voltage　fluctuations　of　RMS　values　are　quite　different　from　those　of　modulation　wave　with　the　increase　of　frequency.　The　new　comparison　table　based　on　RMS　values　should　be　adopted　to　calculate　flicker　value　correctly.　Finally,　consistent　conclusions　can　be　drawn　when　the　above　analysis　is　extended　to　multiple　modulation　wave　frequencies.