To help solve protection performance problems of wind farm transmission line pilot protection in the data delay transmission and abnormal sampling data, this paper proposes a positive sequence impedance amplitude ratio based on pilot protection. By analyzing the positive sequence impedance amplitude characteristics of the wind power system transmission line inside and outside area, it is concluded that the positive sequence impedance amplitude difference ratio characteristics of the double-ended positive sequence impedance are different under the fault inside and outside area. The balanced iterative reducing and clustering using hierarchies (BIRCH) clustering method is introduced to remove the abnormal sampling data from the positive sequence impedance magnitude sequence and form the fault time series clustering features without abnormal sampling data. This is combined with the double-ended positive sequence impedance magnitude difference ratio features to construct the pilot protection criterion. This is not affected by the data delay transmission. The simulation results show that the proposed pilot protection is not affected by system operating conditions, fault type, data delay transmission nor abnormal sampling data. The proposed pilot protection can still correctly identify the fault direction when the transition resistance reaches 150 Ω. It has strong noise immunity and is suitable for weakly-fed power systems with wind power access.