Abstract: The fault characteristics of AC transmission lines are significantly influenced by the access of wind farms and DC systems, rendering traditional relay protection principles inapplicable. In this paper, we propose a new principle of pilot protection for wind power transmission line based on difference of mode power. Firstly, on the basis of the single unit model, the short-circuit current expression of the doubly-fed wind farm is derived considering the interaction between the various devices of the wind farm. The establishment of a mode power calculation model for the back side system feeding to the transmission line is complemented by incorporating DC system network topology. The protective criterion associated with the mode difference and model difference is constructed by utilizing the characteristics of the fault network topology change outside the zone, aiming to identify fault sections. Finally, the proposed method is validated through experimental results conducted on the RT-LAB platform.