In a microwave circuit system, the discontinuity caused by electromagnetic wave entering into another transmission medium from one transmission medium will greatly affect the transmission performance of the system, which has always been the focus of microwave circuit design. When the electromagnetic wave band enters into the millimeter wave and terahertz band, how to realize the efficient and low loss transmission of electromagnetic wave from the metal rectangular waveguide interface to the dielectric substrate is the key to the realization of millimeter wave terahertz communication system. Substrate integrated waveguide to rectangular waveguide transition structure is an important structure connecting waveguide interface and planar circuit in millimeter wave and terahertz communication system, and it is the basis of designing planar antenna array. In this paper, a W-band and D-band substrate integrated waveguide to rectangular waveguide transition structure is designed, which improves the transmission performance and expands the bandwidth through the stepped structure. On this basis, a one-in-two divider structure is designed, with an empty cavity structure used to reduce the loss and expand the bandwidth. These two structures have the characteristics of simple structure and easy processing, and their practicalities are verified by simulation optimization and actual low temperature co-fired ceramic substrate processing and assembly test. The actual test results show that the substrate integrated waveguide to rectangular waveguide transition structure can achieve a return loss of less than –10 dB in a frequency ranges of 126–149 GHz and 112–139 GHz, the one-in-two divider structure can achieve a return loss of less than –10 dB in the frequency band of 132–155 GHz.