The purpose of this research is to establish the crosstalk characteristic of mm-wave Coplanar structure. The components in mm-wave CPW are classified to transmission devices, EM devices, and quasi - TEM devices. After design of these devices, we analyzed these CPW s electromagnetically using FDTD method, and suggested the corsstalk characteristic of mm-wave CPW. In oder to realize a CPW module up to 30 GHz-100 GHz band, we research on a technology of 3-dimensional mm-wave CPW, and GaAs substrate with ohmic lossy layer. As a result this research, we suggested the optimum crosstalk characteristic of mm-wave CPW, and improved the crosstalk quality of mm-wave CPW.