Abstract: Modular multilevel converter based high voltage direct current（MMC-HVDC） is especially suitable for supplying power to weak AC grid due to its self-commutation capability. When the strength of the AC system is reduced, it will restrict the DC power transmission capacity of the system, and even lead to instability. Aiming at the problem of limited power transmission of MMC-HVDC system integrated to weak AC grid, we established a state-space and DC impedance model and studied the influence of strength of AC grid on DC power transmission capability from both time-domain and frequency-domain to reveal the reason for the limited power transmission under weak AC grid conditions. An improvement method of power transmission capability with DC current feedback introduced in the constant DC voltage control link was proposed based on the results of participation factors. We analyzed the mechanism of improving the control strategy from both time-domain and frequency-domain, respectively, and obtained the feasible range of control parameters and the maximum improvement level of power transmission capability quantitatively. This method effectively improves the DC power transmission capability of MMC-HVDC system while avoiding steady-state errors.