Abstract: Schottky diode detector is one of the key devices of THz wireless communication system. In order to make further research on the nonlinear characteristic of a Schottky diode detector (SBD), a model was established based on Ritz-Galerkin method. Meanwhile, the model has been used to predict the output and the sensitivity of the detector, which indicates this model can precisely predict the performance of the detector. Finally, the influences of the power levels, load resistance and temperature on nonlinearity behavior of the SBD in 0.34 THz were investigated by this model, which indicates that the diode detectors exhibit true square-law to a linear law with an increase of power level is correct only under restrictive conditions, and that slopes corresponding to higher-order effect can be easily encountered in practical situations.