Abstract: There is a problem that the sensitivity of multi-terminal flexible HVDC line travelling wave protection is insufficient when the fault of the remote end is high resistance. Firstly, this paper analyzes the characteristics of the line mode current wave in the internal and external faults of the flexible HVDC line, and constructs the direction criterion according to the forward wave and the inverse traveling wave. Secondly, through the construction of line transfer function, the first traveling wave expression of fault current at protection installation is analyzed when different faults occur. On this basis, the parameters of the measured signal are identified, the current reference function inside and outside the region is constructed, and the fault identification criteria inside and outside the region is constructed using the difference between the measured data and the calculated data. Finally, fault pole selection is realized based on the weighted ratio of fault components of positive and negative current. The simulation results of PSCAD show that the scheme can reliably identify faults inside and outside the line area, and has high resistance to transition and certain anti-noise interference ability.