Terahertz electromagnetic radiation (from 0.1THz to 10THz) that lies in the boundary region between light and radio waves has attracted much attention in recent years due to its certain extraordinary properties. This paper presents the design and simulation investigation of a 0.66THz low-loss subharmonical mixer based on GaAs Schottky barrier diodes. The antiparallel diodes pair is fabricated from China Electronics Technology Group Coporation-13 Institute, flip-chip mounted on a 25um-thick gallium-arsenide substrate. The simulation results exhibits that the conversion loss of the mixer is below 10 dB in the band from 0.6THz to 0.7THz.