Abstract: Terahertz solid-state Schottky harmonic mixing technology is an important means of space astronomy, planetary exploration, and atmospheric detection. Obviously, the research on terahertz monolithic integrated harmonic mixers is of great significance, as it overcomes a series of problems such as assembly difficulty, thermal imbalance, and poor reliability that exist in traditional hybrid integration methods (discrete Schottky diodes are glued to quartz matching circuits). Based on the domestic gallium arsenide process line, the development and verification of a 550 GHz monolithic integrated harmonic mixer are independently completed. For diode design, accurate nonlinear and 3D models of Schottky diodes are established. For circuit matching, typical structures are adopted, such as reduced height waveguides, stepped impedance lines (to isolate RF and LO signals), rectangular probes. Combined with field-circuit analysis methods the simplest matching circuit design is realized. The mixer circuit includes diodes integrates on a 3 μm GaAs thin film, and is fixed with the cavity through the beam leads on both sides. The test results show that the single sideband conversion loss of the mixer is better than 13.4 dB at 548~572 GHz. Based on this result, a feedback simulation study of the design is achieved.