Many four-parallel lines on the same tower show the asymmetry of parameters. A new phase-mode transform introduced is introduced to totally decouple the asymmetric matrix and improve the accuracy of fault analysis of four-parallel lines. Referring decoupling method of existing phase-mode transformation, four zero-sequence component method (FZCM) is proposed. Keeping positive and negative sequence components unchanged, this method introduces a same-direction component and three circulation components with correction factors to decouple the matrix. FZCM can be applied to fault analysis of asymmetry-parameter four-parallel lines under same voltage grade or different voltage grades. Fault sequence network can be figured out by the sequence component definition and fault boundary condition. Simulation results prove the validity of four zero-sequence component method for fault analysis.