Abstract: The integration of fast frequency modulation control into the control system of doubly fed induction generators (DFIG) is conducive to improving the frequency stability of high-proportion new energy power systems. The aforementioned condition, however, may lead to small-disturbance instability on the electromechanical time scale. To investigate the electromechanical time scale stability of DFIG connected to AC power grid with frequency modulation control, firstly, an electromechanical time scale dynamic model of DFIG with fast frequency modulation control is established by combining dynamic theory and internal potential definition. Then, an electromechanical time scale small signal model of DFIG and synchronous machine system is derived. The modal analysis and participation factor analysis are employed to investigate the changing trend of the dominant mode of the electromechanical time scale of the DFIG with frequency modulation control, which is connected to the AC grid. The research aims to study the influence of external grid factors and internal control factors, and reveals their influence on the electromechanical stability of the grid-connected system. The accuracy of the mathematical model and the effectiveness of the proposed method are ultimately verified through time domain simulation of the doubly-fed wind turbine-synchronous machine.