In order to reduce the size of electromagnetic interference (EMI) filter and improve the power density of switch mode power supplies, the elliptic planar LC coil structure is proposed in this paper. The finite element simulation of the rectangle and elliptic planar LC coil is done. By comparing the simulated results of these two coils, it can be seen that the elliptic planar LC coil may be used as the basic EMI filter unit, as well as planar passive EMI filter. The high-frequency common-mode equivalent circuit model is established taking into account the EPC of common-mode inductor and the ESL of common-mode capacitor and their ESR. The insertion loss formulas are deduced with matrix of two-port network. The simulation and prototype experiment results are presented showing the effectiveness of the new integrated EMI filter structure and its high-frequency common-mode equivalent circuit model and insertion loss formulas.