With the penetration level of wind power into the gird continuously increasing, the impact of wind farms on dynamic stability of power systems is significantly highlighted. It is necessary for grid-connected wind farms to provide ancillary services, such as active power control, frequency regulation and damping control. Currently, most of the published papers have already studied the virtual inertia control and its effects on improving the stability of system frequency and small-signal stability. A frequency control loop is added to the active power control system of wind farms, which can be utilized to make wind farms have the ability of fast response to system frequency deviation following the appearance of the power imbalance, thus increasing the stability of system frequency. This paper summarizes the influencing characteristics of different virtual inertia control strategies, various control parameters and their effects on system small-signal stability and torsional oscillations. Furthermore, the control architecture, designing of the controller and integrated methodology with damping control are deeply studied. The research hotspots of virtual inertia control and its development trends are introduced. This paper also presents some issues to be researched in the near future.