This paper presents a novel fault location principle for HVDC transmission lines using two terminal data. Based on a distributed parameter model， the voltage distributions are calculated by the voltage and current measured in each terminal， respectively. And the fault can be located by the calculated voltage distributions. The algorithm performed in the time domain needs a very short data window and has satisfactory accuracy in practice. The effectiveness of the algorithm proposed is verified using the field data and the simulation data by the frequency-dependent line model in PSCAD. The results show that any fault of the HVDC transmission line can be located quickly and accurately.