This paper introduces the six sequence variables method to analyze the electrical signals gained from the end of transmission lines， and uses the same positive sequence signal's long line equation to locate the fault point. With the help of long line equation， the fault currents can be calculated form the location of fault and electrical signals gained from the end of transmission lines. Based on the magnitude characteristics of fault currents， a theory of fault phase selection is proposed. This principle is clear and reliable. It can automatically adjust the criterion of fault phase selection when the operation mode is changed. Theoretical analysis and MATLAB simulations show that this method has high fault locating accuracy and is not affected by distributed capacitance and transition resistance. It can provide effective fault phase selection logic for distance relay protection of parallel transmission lines. Analysis result of real fault data using this method shows that it is practical and reliable.