ABB and SIEMENS schemes based on the voltage change rate are the existing main protection for HVDC transmission lines. But the analysis and simulation tests show that these protection schemes may be unreliable as high impedance faults or as disturbances of above 2% noisy. The paper presents a new protection scheme of traveling wave current polarity comparison for a bipolar HVDC transmission line. The traveling wave current polarity is represented by the wavelet modulus maxima (WMM) of the fault current traveling wave. The traveling wave current polarity comparison protection scheme is evaluated by PSCAD. The extensive simulation studies show that the proposed scheme is reliable to distinguish internal faults from external faults of HVDC transmission lines. And the protection scheme is immune to high impedance faults and able to accurately detect the fault line under the electromagnetic coupling circumstance.