In order to improve the low-voltage ride-through（LVRT）capability of permanent magnet synchronous generator（PMSG）under weak grid, this paper proposes a low-voltage ride-through control strategy for power support and auxiliary protection of unloading circuits based on power grid impedance characteristics. Based on the equivalent phasor diagram of power grid, the relationship between impedance characteristics and voltage support effect is derived, and the optimal power regulation strategy is designed accordingly. When asymmetric faults are considered, positive sequence voltage is supported optimally and negative sequence voltage is suppressed optimally. Based on the proposed strategy, the low-voltage ride-through ability of the PMSG is maximized to reduce the risk of large area cutting of the power grid and ensure the reliable operation of the PMSG. Finally, a simulation model of PMSG grid-connected system is built in MATLAB/Simulink to verify the feasibility of the proposed strategy.