Green new energy is developing rapidly, with increasing integration in a clean and efficient wind power industry. However, large-scale off-grid events of wind turbines have occurred from time to time, posing new challenges to the level of control of new energy sources. A method is proposed for an online evaluation criterion for off-grid risk to deal with the difficulty of coordinating the steady-state cut-off strategy with wind power off-grid and the difficulty in judging the off-grid index. Based on the electrical quantity and protection action information of each unit, the risk of an off-network under low-voltage-ride-through mode of wind farm is evaluated taking the wind farm as a whole. The method realizes panoramic monitoring and evaluation of the wind farm fault process, laying the foundation for precise control and cut-off execution. Finally, the effectiveness of the proposed de-networking risk assessment criteria is verified by simulation. This work is supported by Youth Fund of National Natural Science Foundation of China (No. 51507077).