When the VSC-HVDC transmission system is employed to the weak grid, which is comparatively lower or no inertia, hence the large transient frequency deviation problem is always happened under the disturbances. In order to increase the inertia of the receiving grid, this paper proposes a emulation inertia control strategy, which significantly improves the system frequency quality. Based on the comparisons between the DC capacitance of the converter and the energy storage features of synchronous generator rotor, the relationship between DC voltage and system frequency is built. And then the specified formula for the emulation inertia calculation is given. The inverter station of the VSC-HVDC system with conventional control strategy and the proposed emulation inertia control strategy respectively is tested under different disturbances using PSCAD/EMTDC. Simulation results show that the proposed emulation inertia control strategy can better suppress the fluctuation frequency under the disturbances and improve the system frequency quality.