Aiming to develop terahertz multi-band high sensitivity receiver, a broadband 0.67 THz sub-harmonic mixer is developed based on the nonlinearity of terahertz GaAs plannar Schottky diode and quartz film thinning process. The influence of the performance parameters of Schottky diode on the performance of terahertz mixer is analyzed, which provides a theoretical guide to diode selection and mixer evaluation. In the design of 0.67 THz sub-harmonic mixer, the synthetic design method is adopted by using the electrical and electromagnetic simulation software, and the optimization is made on the coupling between the discontinuous microstrip and waveguide in order to minimize the conversion loss. In the design of 0.67 THz sub-harmonic mixer, the best simulated conversion loss is less than 7 dB over 0.62-0.72 THz frequency range, the LO drive power is less than 4 mW, and the isolations are above -30 dB between LO port and IF port, RF port and IF port.