Considering the low voltage ride through（LVRT）requirement and weak-infeed feature of wind farms，the fault characteristics of a centralized wind farm is analyzed firstly based on doubly-fed wind power generation system.Since the Crowbar protection contributes to the positive and negative sequence impedances，especially the former，the wind farm weak-infeed characteristics are strengthened.On that basis，the performance of distance protection of wind farm grid connection line is analysed.The results show that the Crowbar and weak-infeed property of wind farm may cause wrong phase selection and affect the precision of impedance protection relay.Some countermeasures are also proposed.Finally，a doubly-fed wind farm is simulated，and the simulation results demonstrate the validity of the theoretical analysis.