Abstract: Harmonic state estimation is of great importance for power quality management. Most of existing methods assume the harmonic phasors at different locations are available, which do not consider the practical challenges such as the synchronization and the real-time data transmission. As a result, these methods can hardly be used in practice. In view of this, this paper proposed a new harmonic state estimation algorithm that suits for asynchronous power quality monitoring system in China. In the proposed method, the non- synchronization issue was addressed through phase angle error compensation, and the trust region algorithm was applied to solve the nonlinear least-square problem. In addition, a new observability analysis method was proposed to ensure the applicability of the method in practice. Finally, the performance of the proposed model was verified by simulation studies using IEEE 30 node system and the real-life field measured data. The result indicates that the proposed method can deal with the asynchronous harmonic measurements and its performance is better when the load fluctuation is small. Furthermore, the trust region algorithm is proved to be effective through the comparison with other nonlinear least square algorithms.