Abstract: The interception failure of a wind turbine blade lightning protection system will seriously affect the safe operation of a wind turbine. Broken faults often occur in the connection between the branch and the main down conductor of most wind turbine blades. In this paper, a method is proposed to detect and locate the branch broken fault in the blade down conductor of wind turbine, based on the principle of traveling wave transmission. First, through theoretical analysis and simulation, the influence of the propagation process of the nanosecond pulse signal in the multi-branch structure of the blade down conductor on the identification of the fault-reflected wave is discussed. Then, in order to solve the problem that the fault reflected wave is hidden in the fault waveform, the "difference deduction method" is introduced. And according to the characteristic that the amplitude of the pulse cluster generated at the fault branch structure changes, the fault reflected wave is extracted by the difference, and the fault branch point is located by looking for the fault reflected wave in the difference waveform. Finally, a blade down conductor of a 2.5 MW real wind turbine is employed to verify the proposed method and the experimental results prove its effectiveness. The proposed method has good applicability and can be applied to detect and locate the branch broken fault in blade down conductor of any type of wind turbine.