Among variety THz application systems, the THz mixer is a key component of the receiver front-end, and the Schottky diode is the most important part of the mixer. This paper applies the integrity of signal to analyze the characteristics of Schottky diode. Based on analyzing the discontinuity of the pad and the parasitic capacity, a circuit based module is put forward. Then the model of Schottky diode is set up according to the designed physical parameters,including size,the dielectric constant of the material of the Schottky diode etc. The rationality of the equivalent circuit is proved by comparing the S parameter generated by High Frequency Structure Simulator(HFSS) and the simulation result of a circuit based model generated by Ansoft-designer. The model can be applied to the circuit-level simulation of terahertz mixer.