Harmonics　pose　a　great　threat　to　safe　and　economical　operation　of　power　grids.　Therefore,　it　is　critical　to　detect　harmonic　parameters　accurately　to　design　harmonic　compensation　equipment.　The　fast　Fourier　transform　(FFT)　is　widely　used　for　electrical　popular　power　harmonics　analysis.　However,　the　barrier　effect　produced　by　the　algorithm　itself　and　spectrum　leakage　caused　by　asynchronous　sampling　often　affects　the　harmonic　analysis　accuracy.　This　paper　examines　a　new　approach　for　harmonic　analysis　based　on　deducing　the　modifier　formulas　of　frequency,　phase　angle,　and　amplitude,　utilizing　the　Nuttall-Kaiser　window　double　spectrum　line　interpolation　method,　which　overcomes　the　shortcomings　in　traditional　FFT　harmonic　calculations.　The　proposed　approach　is　verified　numerically　and　experimentally　to　be　accurate　and　reliable.