Basic problems of the EMI mains filter is explained in the introduction of this thesis. These problems appear during the measurement of insertion loss of filters and by design of EMI mains filter. The important problem is uncertainly of the terminating impedances. Eventualities measurement insertion loss of EMI mains filter and motivation of creation filter models are shown. The following part of this project shows the electronic components, from which are realized the EMI mains filter. Parasitic properties of these real devices are also discussed. The circuitry of EMI mains filter is described by the Modified Nodal Voltage Method. The optimization method called Participle Swarm Optimization is introduced, too. Basic principle and terminology are mentioned. The third part of this project is focused on the own filter and spurious components. Influence of own filter and spurious filters components on insertion loss curve are showed. Magnetic factor coefficient k is searched by the optimization method PSO. The last part of this thesis deals with creation of the alternative circuits with spurious filters components. The performances of the alternative circuits were compared with the measured data for symmetrical and asymmetrical measurement setup. The breakages in the insertion loss curve were used for determining the spurious components.