With the electric power industrial development, electric power device was abroad using as the core of switch converter. For a clear near-field characterization quantitative electromagnetic interference of converter circuits, this paper applied finite element method to analyze a Boost circuit. Transform topology structure of circuit and build corresponding entity finite element modeling. Quantitative analysis for different topology structure electromagnetic distributing and near-field characteristics, and it become clear that the distribution and the role of electromagnetic field of the circuit through the results. The objective of the analysis is to provide the principle and put a new way for the Layout and component design of the power electronic circuits, at the same time above research works make a foundation for further studying EMI problem of the power electronic devices and are of academically and application worthiness.