Raditional fluctuation method estimates the utility harmonic impendence by the ratio of the harmonic fluctuation of voltage to current at PCC, in which fluctuation samples are selected to improve average accuracy. However, the fluctuation filtering method may not increase estimation accuracy of individual sample. This paper proposes an improved fluctuation method based on the phase angle correcting principle. First, the phase angle value estimated by harmonic fluctuation ration of voltage to current is modified. Then, an extension line pointing the actual value of utility harmonic impedance is drawn from estimated dot by use of the corrected phase. The intersection of different extension lines is calculated to approach the actual value. Simulation shows that the improved method in this paper provides a more precise estimation than that provided by traditional fluctuation method in the case that the customer fluctuation is dominant. This method provides an effective way for the estimation of customer harmonic emission level.