In the terahertz band, diode size can no longer be ignored compared with the wavelength, significant parasitic parameters will be introduced due to diode package, so it is very necessary to establish three-dimensional model to extract parasitic parameters. Meanwhile manual assembly becomes more difficult, circuit uncertainty will increase. A 330GHz GaAs monolithic integrated sub-harmonic mixer based on planar schottky barrier diode designed by China Electronics Technology Group Corporation-13(CETC-13) and University of Electronic Science and Technology of China(UESTC) fabricated on 12um thick suspended GaAs substrate was presented. Test results show that the minimum conversion loss is 10.4dB at 328GHz, SSB conversion loss was less than 14.7dB from 320GHz to 340GHz when the LO power is 5mW.