Abstract: In a high-proportion new energy power system, the dynamic interaction between the inverter and the grid makes the system harmonic resonance problem prominent and increasingly complex. This paper takes the three-phase balanced system as the research object, studies the overall sequence impedance modeling method of the grid-connected system considering the positive and negative sequence frequency coupling and the interaction between the inverter and the grid impedance under the abc coordinate system, so as to avoid the determinant calculation. This paper pioneers the overall impedance measurement method of the grid-connected system. Furthermore, on the basis of the overall impedance model, a frequency-domain impedance stability criterion and an oscillation frequency prediction method are proposed, which can establish the connection between the frequency-domain impedance criterion and the physical links of the grid-connected system, in order to greatly reduce the risks of misjudgment. Finally, the correctness of the overall impedance model of the system is verified by frequency sweeping through MATLAB/Simulink simulation. RTLAB hardware-in-the-loop experiments proves that it can be used to judge the stability of grid-connected systems, and has the advantage of high accuracy of resonant frequency prediction.