This paper proposes a method based on scattering parameters (SP), genetic algorithm (GA) and self-organizing migrating algorithm (SOMA) to extracting the impedance information of noise source and obtain its equivalent RLC parameters. Firstly, extracting equipment under test (EUT) impedance by using SP method. According to the advantage of fast convergence speed, GA is used to preliminary optimize the impedance information such as amplitude and phase, and take the obtained value of equivalent RLC parameter as the initial value to be further optimized. Finally, taking SOMA to further optimize the initial value obtained by GA according to the characteristic of high precision, and the optimal RLC parameters can be derived. This method can obtain the equivalent RLC parameters accurately and quickly, which can give a reference for the design of conduction electromagnetic interference (EMI) filter.