In this paper, the terahertz (THz) detection based on Silicon MOSFET is investigated with two-dimensional (2D) ensemble Monte Carlo (MC) simulation study. The analytical model of responsivity to high frequency small signals based on the small-signal equivalent circuit of MOSFETs operating in terahertz detection mode are developed and calibrated. We explore the impacts of input excitation signals with different frequency and amplitude on THz detection. Moreover, it is shown that the responsivity to THz excitations could be controlled by modulation of the gate voltage and the gate length in the MOSFET.