With large-scale wind turbines connected to the power system, the power grid strength becomes weak, leading to unstability problem of wind turbines in DC voltage control timescale. The stability limit of double-fed induction generator (DFIG) system connected to weak AC grid is studied in this paper. Firstly, the relationship between the active power and terminal voltage of DFIG injected into the power grid and the current of the dq axes of the rotor as well as the physical constraints of the stability limit are studied, and the sensitivity is analyzed. The sensitivity of active power to rotor d-axis current is summarized. Then, a small-signal model of DFIG connected to weak grid is built. Through the eigenvalue analysis, the influence of the dynamic behavior of the control loop of DFIG on its stability limit is studied. The results show that the stability limit can be increased by decreasing the bandwidth of the phase locked loop (PLL) or increasing the bandwidth of the terminal voltage control loop with equal damping in the normal operating range, when the dynamic process of all control loops is considered. Without considering the dynamic reactive power support, the power angle of DFIG is limited to about 50°. Considering the dynamic process of all control loops, the limit of the power angle of DFIG is about 60°.