An equivalent circuit model of mixing Schottky diode with cut-off frequency of 5 THz was reported based on DC measurement and 3-D electromagnetic(EM)simulation combined of EM simulator and circuit simulator. The model of nonlinear Schottky junction and 3-D periphery structure full-wave simulation model was researched carefully, the four-ports model considered real circuit topology was established. The equivalent circuit model can be used for design of mixers worked at the lower end of terahertz band, the methodology of this diode model was a reference of much more higher terahertz frequency. A sub-harmonic 220 GHz wideband mixer was designed based on the model, the double sideband conversion loss was less than 10 dB in the range of 192 GHz to 230 GHz, the measured result was well with the simulated result.