Abstract: The accuracy of harmonic emission level assessment of residential loads is affected by background harmonics or three-phase harmonic unbalance. Based on Norton’s and Davinan’s theorem, a model is constructed for assessment of harmonic emission level. An analysis is carried out on the problems of fluctuation method applied in harmonic impedance estimation of residential load distribution network and the influence mechanism of three-phase unbalance on the system harmonic impedance estimation. A system harmonic impedance estimation method is proposed by combining the harmonic main sequence characteristic extraction and the selection of fluctuation coefficient. The equivalent method of load harmonic impedance and the influence of its estimation error on the calculation of harmonic emission level are discussed. The results of simulation and engineering application show that the 95% confidence interval of the estimated harmonic impedance converges significantly, and the assessment result of harmonic emission level is more accurate.