Aiming at the problem of low frequency and voltage stability of power system leading to grid connection failure during pre-synchronization of GFM converter, a pre-synchronization Control strategy of GFM converter based on improved Linear Active Disturbance Rejection Control (LADRC) is proposed. Firstly, the Phase Locked Loop (PLL) control strategy based on phase Angle compensation is used to synchronize the phase and amplitude of the grid voltage with the feedback control of phase deviation, which can avoid the stability problems caused by the low precision of the PLL and the slow response speed. On this basis, the introduction of LADRC in the angular frequency output of the active frequency branch can effectively suppress the frequency oscillation of the system, so as to ensure the normal pre-synchronization process of the GFM converter and realize the successful grid-connection. Finally, a GFM converter pre-synchronization and off-grid model based on improved LADRC was built in MATLAB/Simulink platform, and simulation verification was carried out. The results show that the proposed strategy can improve the voltage and frequency stability of the power system, accelerate the system pre-synchronization process, and ensure the safe operation of the GFM converter and finally achieve successful grid-connection, the effectiveness of the proposed method is verified.