Flexible DC technology has revolutionary significance in flexibly solving the problem of high proportion of new energy consumption. Due to the vulnerability of high-ratio power electronic equipment and the difficulty in extracting fault information,traditional line protection schemes can no longer be reliably adapted to the flexible DC transmission system. A rapid protection scheme for flexible DC transmission lines based on voltage traveling wave steepness is proposed in this paper. By analyzing the transient characteristics of DC line faults,and utilizing the differences in the steepness and polarity of fault voltage traveling waves on both sides of the current-limiting reactor, the range of effective transient information extraction is increased,and the fault identification inside or outside the region is realized. The faults are classificated by utilizing the significant difference in the degree of voltage traveling wave variation between the faulty and sound poles. Lightning interference is considered and a rapid identification method is proposed by using its initial change characteristics. Finally,the performance of the protection scheme under various influencing factors is verified by simulation,which can identify faults quickly and reliably and has good sensitivity and anti-interference ability.