Abstract: DFIG-VSG (doubly-fed induction generator-virtual synchronous generator) based on rotor inertia control has gained popularity in engineering application. This approach can guarantee the economical operation of wind turbine and provide effective frequency support to the grid meanwhile. The adaptation of frequency regulation by DFIG-VSG is analyzed and speed restoration methods which are suitable for engineering application are studied. First, influencing factors on support time of DFIG-VSG utilizing rotor inertia control is analyzed. Thus general range of support time of wind turbines are given. Second, constant-value and comprehensive speed restoration methods are proposed, followed by comparing them with conventional MPPT curve restoration. Comprehensive speed restoration can inhibit second frequency drop significantly. Frequency regulation characteristics of DFIG-VSG is simulated in Simulink where wind turbines are connected with synchronous generator. Comprehensive restoration method is then testified.