The utility model provides a terahertz is mixer circuit now based on single scale intergration technique, includes radio frequency 3dB branch waveguide directional coupler, 135 degrees phase shift 3dBbranch waveguide directional coupler of local oscillator, coaxial probe, IF coupling ring, intermediate frequency signal and two terahertzs subharmonic first detector now, does terahertz subharmonicfirst detector now include the radio frequency plumbing be microstrip transition, single scale intergration schottky diode to, local oscillator waveguide microstrip transition, IF filter and local oscillator low pass filter, wherein, the diode pair of single scale intergration schottky diode to being the reverse parallel connection. The utility model discloses the terahertz harmonic mixer amongthe mixer circuit now adopts semiconductor technology to obtain, but the size of accurate control diode position and microstrip circuit, and the error far is less than manual assembly, has greatly reduced the influence of assembly error to the mixer circuit performance, simultaneously, this mixer circuit can effectively eliminate the local oscillator noise, has improved the noise performance and the efficiency of system.