HVDC transmission lines and their boundaries have obvious attenuation effect on the high frequency components of fault transient signals. This fault feature is widely used in transient protection. Studies have shown that compared with line boundaries, the attenuation effect of long lines on the high frequency components of fault transient may be greater. In order to avoid the protection malfunction caused by this situation, the commonly used fault feature extraction methods are currently used. In order to obtain energy ratio by using different scales of wavelet transform. However, the algorithm of transient protection based on wavelet transform is relatively complex and the mode of fundamental wave selection is not uniform. Therefore, a new ratio algorithm is proposed to simplify the process of fault information processing for DC lines by replacing the low frequency component with the full current for the energy ratio of fault transient signals. A new fault location method for DC lines is designed, and the fault pole can be judged directly by using this criterion. A lot of simulation results in MATLAB prove that the protection algorithm can correctly reflect the fault characteristics, has simple logic and can act quickly and reliably.