When the oscillation suppression measures on the new energy side fail,the sub-synchronous oscillation induced by the interaction between the double-fed wind farm and the series compensation will result in grid disconnection of a large number of wind-driven generators,causing adverse effect on system stability. Since the existing measures cannot guarantee reliable oscillation suppression under any circumstances,it is necessary to take the initiative to conduct emergency control of the wind field at the network side. On the basis of frequency domain impedance,an emergency control strategy is formulated to address the problem of excessive real-time calculation during slicing of radial network,so as to reduce the amount of calculation and decision-making time. The relationship between the real part of the frequency domain impedance and the mode value,phase angle of branch impedance at the new energy side under the polar coordinate system is deduced,followed by a three-step judgement depending on the change of the real part. Firstly,the 'suspension of invalid units' is excluded. Secondly,the valid units with effective emergency control are selected from the rest units. Thirdly,the order of suspension is determined based on the size of projection of the complex impedance,so as to prevent excessive suspension. On the basis of the actual parameters of transmitted grid after series compensation at a domestic wind field,the effectiveness of the proposed strategy is subject to PSCAD simulation. The simulation result shows that emergency control with adoption of the proposed strategy herein can effectively improve the system damping during the sub-synchronous oscillation and prevent rapid divergence of oscillation.