To avoid a trial and error adjustment for designing EMI filters ideally, clarifying load impedance of operating condition, ie dynamic impedance of equipment is very useful. Therefore request to non-contact measurement method of the impedance connected to a wire harness is increasing rapidly. A measurement method using network analyzer together with two current probes were previously proposed. However it is confirmed only up until 30MHz regrettably. There are many radio equipment using frequency above 30MHz such as AM/FM receiver, GPS receiver installed in the vehicle. So expansion of measurement frequency is indispensable for the auto industry. As the first step, we tried to expand applicable frequency to 100MHz, FM band. In this study, we applied transmission line theory to the above mentioned non-contact measurement method. Furthermore, in order to use the theory, characteristic impedance and phase constant of the wire harness are necessary. So we also proposed a method to estimate them by one additional measurement data. The load impedance was measured with an error within 10% up to 100MHz. As a result the validity of the newly proposed measurement method was confirmed experimentally. Accordingly the possibility of the appropriate EMI filter design efficiently in the FM band was found.