Abstract: With the wide application of n jointed parallel lines on the same tower, the fault analysis problem for different type transmission lines is solved based on the six and twelve sequence component method. The six and twelve sequence component methods can be used to decouple the mutual inductance between lines completely. The method of parameters' modification applicable to mixed n jointed parallel line system is proposed based on the decoupling of inter phases and inter lines. When faults occur in parallel lines and in four jointed lines, short circuit currents of many types of single line faults and inter line faults are calculated according to the method of electrical parameters' modification. The correctness of this method is validated by comparing the calculation values with the ATP simulation values.