Abstract: The stability of the grid-connected inverter (GCI) system under weak grids is deteriorated due to the asymmetric positive-feedback mechanism introduced by the phase-locked loop (PLL) structure. Under the same main circuit parameters and control loop parameters, the small-signal models of the control loop of GCI in dq domain and αβ domain were constructed respectively. It showed that the positive-feedback loop introduced by PLL in the αβ domain was less than that in the dq domain. By comparison, the reason why the stability of the GCI system in the αβ domain was stronger than that in the dq domain was analyzed. Meanwhile, by analyzing the position difference of the asymmetric positive-feedback loop introduced by the PLL structure in the small-signal model, the influence degree and mechanism of the asymmetric positive-feedback loop in different positions on the stability of GCI were revealed for the first time. Finally, simulations and experiments verified the correctness and effectiveness of the theoretical analysis.