In this paper, we propose a parameter optimization algorithm for EMC macro-modeling of IC/LSI power currents called the LECCS (Linear Equivalent Circuit and Current Source) model. The unnecessary electro-magnetic wave from a digital electronics device may cause the electromagnetic interference (EMI) to other apparatus. Thus, its reduction has been regarded as one of the highest priority issues in digital electronics device designs. In order to accurately simulate high-frequency currents from power-supply sources that are the primary sources of EMI, the LECCS model has been proposed as a linear macro-model of a power-supply circuit. A LECCS model consists of multiple RLC-series circuits in parallel to represent the equivalent circuit between the voltage source and the ground. Given a set of measured impedances at various frequencies, our proposed algorithm first finds the number of RLC-series circuits corresponding to the number of valleys. Then, it searches optimal values of RLC parameters by a local search method. The effectiveness of our algorithm is verified through applications to a real system, where the accuracy and the required processing time by our algorithm are compared with the conventional method.