Double-circuit lines on the same tower with asymmetrical parameters can not be decoupling with traditional six-sequence components. To solve this problem, a new decoupling method is proposed. Three phases are decomposed to positive, negative and zero sequence component first, but there are mutual inductance between zero sequence component. Then the zero sequence is divided into the same direction component and the reverse component. The method solves the problem of zero sequence mutual inductance of double circuit lines on the same tower with asymmetric parameters. When a line fault occurs, the relationship between the current components can be found out by the boundary conditions. If a fault occurs on different lines, the amplitudes of positive sequence components of two lines are different. If different kinds of fault occur on the same line, the amplitudes of six-sequence component have corresponding relation. If a fault occurs on different phases with the same types, the six-sequence component' phase is different. This paper proposes relevant phase selection criterion according to the above relations, and also gives its procedure and method. PSCAD simulation results show that the method can accurately measure the phase of fault and is not affected by the type of fault, fault location, fault resistance.