Because of the control mode of the doubly-fed fan itself, its own frequency is decoupled from the grid frequency. When the load is disturbed, the system frequency changes, but the energy stored in the fan rotor does not respond to the frequency change as quickly as the synchronous generator. Therefore, large-scale access of fans will reduce the inertia level of the power grid, which is not conducive to the frequency support of the power grid. Based on the investigation of the control methods to improve the fan inertia, this paper sets up the virtual inertia control model and the integrated inertia control model respectively, and finds that both can improve the inertia of the system, and the latter can effectively make up for some deficiencies of the virtual inertia control. In addition, the inertia of fan is quantitatively identified by using the motion equation of fan rotor under disturbance.