The effect of reciprocally mutual electromagnetic fields in multi-conductor systems is always complicated. The phenomenon of electromagnetic interference (EMI) that propagates along the line will cause damage in the insulation of line at the resonant frequencies. Therefore, the precise determination of resonant frequencies corresponding to the actual complex configuration of a multiconductor system plays an important role in design and operation. The paper introduces a study to determine the frequency characteristics of any multiconductor system based on a combination of transmission line and Modal transformation methods. The proposed approach which is built in Matlab/programming, is firstly applied to a simple system with available measure results. The error (<4%) indicates the compatibility between calculation method and measurement. After that, the studied approach will be applied to determine the frequency characteristics of a complex multiconductor system used in practice.