Abstract: The paper introduces the methods and experimental results for reducing the transmission and interconnection losses of terahertz waveguides. At present, rectangular waveguides are mostly fabricated by split metal-block technology, and the loss of waveguides in H-plane splitting is obviously higher than that in E-plane splitting. To suppress electromagnetic leakage and reduce the H-plane waveguide loss, electromagnetic band gap structures or choke groove structures are added on the waveguide splitting surface. Using the traditional CNC milling and metal-block techniques, some specially designed waveguide samples, including the conventional rectangular waveguide, the gap waveguide and the choke waveguide, were fabricated and measured in the 170 GHz~260 GHz band. The experimental results show that the conventional H-plane waveguide loss is 0.074 dB/mm at terahertz frequency due to the discontinuous gap caused by waveguide splitting. The gap waveguide loss is 0.017 dB/mm, but the processing is time-consuming and expensive. The choke waveguide loss is 0.025 dB/mm, and the cost and performance are moderate. In addition, a waveguide flange based on the zero-shaped choke groove is also designed and fabricated for contactless and low-loss terahertz waveguide interconnection applications. Compared with conventional waveguide flanges, the flanges designed in this paper have stable performance and remarkable improvement effect.