With the progress of computer technology, the finite difference Time Domain (FDTD) is a numerical calculation technique for solving electromagnetic problems, which was proposed by K.S.Yee in 1966. His basic idea is to use the differential equation of the field components of the time-domain Maxwell equation to replace the differential equation with difference and iterate each field component. However, this method will significantly increase the computational grid as the frequency increases, making it difficult for the performance of a PC to meet the needs, and relying solely on the improvement of computer performance is not practical. For example, when analyzing waveguide membrane filters, in order to correctly simulate the geometric structure of all the membranes, the grid size of the FDTD grid is selected very small, resulting in a very large number of grids describing the entire waveguide filter. Due to the uniform waveguide transmission line between each two membranes, it is obviously unnecessary to use the same grid as the membrane. People have used non-uniform FDTD grids to solve this problem. When the size of the g rids varies greatly, not only is convergence difficult to control, but it still cannot guarantee the saving of calculation time. Applying the Diakoptics idea to the full wave analysis of microwave circuits, the circuit is divided into several independent parts, and different grids are used according to the specific structure of each part to independently perform full wave time domain analysis on each part. As the grids of each part are uniform, it is easy to ensure the convergence of the algorithm.