A traveling wave protection of bipolar HVDC transmission line based on the second order B - spline wavelet modulus is proposed for the problem that the wavefront is difficult to capture or catch the high precision. Firstly, the transient current traveling wave information of both ends of the positive and negative rectifier inverter is obtained, and the fault pole is selected by calculating the correlation coefficient. Then, the second-order B-spline wavelet function is used to decompose the transient current traveling wave to obtain the modulus maxima. Comparing the polarity of the current traveling wave and the maximum value of the wavelet model to judge the inner and outer faults. And finally determining the wave arrival time according to the position of the modulus maxima to realize the fault distance measurement. PSCAD / EMTDC simulation results show that the proposed method can accurately identify the fault, ranging from high precision and difficult to be affected by factors such as transition resistance, fault type and fault distance.