With an extremely weak grid，grid-connected inverters introduce the grid voltage proportional feedforward control strategy to enhance the amplitude gain in the low-frequency band and suppress the background harmonic interference of the grid.However，when the impedance parameter of the grid increases，the phase margin of the system significantly decreases，and instability occurs.Based on the impedance characteristic analysis method，the internal mechanism of the deterioration of the system ’s phase margin is first revealed，and then proposes to connect a second-order low-pass filter on the feedforward channel in series to improve the system ’s phase margin and retain its gain effect at low frequencies as much as possible.However，since the parameters of the added controller are too complex and not flexible enough by using the traditional parameter design method，an adaptive parameter design method combining online impedance detection technology and a genetic optimization algorithm is proposed to improve the parameter design efficiency and thereby enhance the robustness of grid-connected inverters in extremely weak grid environments.Finally，its effectiveness is verified through simulation and experimental results.