In view of the problem that the detailed model of doubly-fed induction generator (DFIG) considering virtual inertia control is high ordered and difficult to analyse, a reduced-order model for DFIG that is applicable to small-signal stability analysis is presented. First, according to the attenuating speed of each state variable, the dynamic characteristics of different components of DFIG are explored from the time scale perspective. On this basis, considering the electromechanical coupling characteristic of DFIG, the third-order simplified model retaining the dynamic of virtual inertia control and phase-locked loop is derived. Moreover then, the dynamic model of inter-connected system with reduced-order model integration is established. Finally, the attenuation time constant of each state variable of DFIG detailed model is calculated. Simulation tests on the New England 10-generator 39-bus test system verify that compared with detailed model of DFIG, the presented reduced-order model could reflect the dynamic characteristics of power system under small-signal disturbance more accurately, with greatly reduced computation amount.