Injection of harmonic current into power grid will induce harmonic impedance in the power system and the acquisition of harmonic impedance is a worldwide problem. In this paper

the site experimental result of power quality analyzer

according to the feature of 0.4 k V distribution grid in Shanghai

is demonstrated by the use of Fouries series expansion and superposition theorem. The positive sequence

negative sequence and zero sequence impedance of three-phase harmonics based on various operation modes of distribution grid and various switching modes of reactive power compensation cap-acitor are analyzed. And the pollution level of harmonic to the power quality of distribution grid is analyzed further by the harmonic sequence impedance.