With the advance of information society recently, the radio and/or mobile communication industry are going to develop rapidly. A precision of analysis and design for EM structure of these fields is rigorously required and the commercial needs and applications of EM structure with high frequency such as antennas and RF circuits become increasingly. To solve these requirements, the numerical analysis methods of 3-demensional structure with electromagnetic fields have been proposed and researched. Typical methods are MoM, FEM, SDT, FDTD and so on. Since the FDTD method is able to predict the movement of electromagnetic wave in the time domain by differential equation for the finite structure, this method proposed by K. S. Yee has been researched with remarkable attention. It used Maxwell's equation with a differential form for analysis of arbitrary finite construction composed of dielectric substance and conductor. Although analysis of nonlinear circuit by FDTD method has comparatively some advantage due to the time domain calculations, the extended FDTD algorithm expressed the equivalent voltage-source and current-source circuit of nonlinear circuit composed of a lumped element has not been almost researched. Because this algorithm was considered the complicated expression for the lumped devices, the constant stability of time-space step size and the complex of analysis model design. This thesis presents reliability of visual graphic design software to simple analyze the EM structure composed of active and passive devices by FDTD method. This proposed software is called SRANT_FDTD and development of visual graphic software for analysis of the EM structure is attempted the first time in Korea. The FET NE3210S01 of the NEC Co. as an active device is considered in theoretical design and measurements. The visual CAD graphic format realized by GUI technique using Borland C++ Builder language offers easy input, multi window output for various results and real time 3-D animation picture of electric fields. In order to confirm accuracy of the proposed software, the LPF and patch antenna as passive device and the amplifier as active device were analyzed and designed. The calculated results of example structures were also compared with the measured ones as well as the calculated ones by commercial tool. the measurement results are shown reasonable agreement with the calculation ones by the proposed SRANT_FDTD software.