Abstract: The large-scale wind power integration systems in China mostly adopt the long-distance transmission mode, which is prone to the situations that the lines are not transposed or the transpositions are insufficient, resulting in voltage imbalance in the sending systems. Therefore, taking the typical actual wind power grid-connected system as the research object, firstly, this paper establishes the fundamental frequency impedance model of the wind turbine and the line. On this basis, the sequential equivalent circuits of the wind power grid-connected system are formed. Then, from the perspective of positive and negative sequential couplings, the mechanism of voltage imbalance in the phase coupling scenario caused by the asymmetry of the transmission line parameters is analyzed; Secondly, based on the mechanism of voltage imbalance, the influence degree and influence law of the main factors of the source and grid side on the voltage imbalance are analyzed in detail, and a virtual admittance suppression strategy is proposed. Finally, a case study is carried out through the measured data and the MATLAB/Simulink simulation, which verifies the accuracy of the theoretical analysis and the effectiveness of the suppression strategy.