Abstract: Under traditional control strategy, UHVDC transmission system lacks inertia and damping characteristics, so it can't effectively adjust the frequency of AC system dynamically. In order to solve this problem, a VSG (virtual synchronous generator)-based control strategy for UHVDC converter stations is proposed, in which two key parameters, including synchronous generator rotational inertia and damping coefficient, are retained. Meanwhile, the calculation method for frequency in virtual rotor is improved, and the PI controller-based secondary frequency regulation is added. Aiming at the situation of load mutation, a two-terminal VSG system model is built for simulation with Matlab/Simulink. The results show that the proposed control strategy has the characteristics of inertia and damping, which can reduce the amplitude, speed and overshoot of frequency fluctuation, suppress the voltage fluctuation of DC system, and realize isochronous control of frequency.