A novel control strategy based on Lyapunov asymptotically stability theory was proposed to eliminate the influences to VSC-HVDC system by unsymmetrical fault of grid. The mathematical model of VSC-HVDC system in positive and negative sequence coordinates was established under unsymmetrical fault of grid. The effects of the negative sequence component of the power transmission system were analyzed. To remove the second harmonic power fluctuations in transmission lines, a outer loop control scheme for power compensation was designed based on Lyapunov asymptotically stability theory with enlarging the stabilization range of the system. To improve the dynamic response performance of traditional PI control structures, an inner loop current controller considering uncertainties was designed with backstepping method. Under the proposed control strategy, the operation conditions of VSC-HVDC system were simulated in the Matlab / Simulink environment for short-circuit ground faults at two-phase AC-side. The results show that the second harmonic power fluctuations of transmission lines can be effectively suppressed by the proposed control strategy with good control performance.