This article uses the Miller model to simulate the ferroelectric polarization of the metal-ferroelectrics-insulator-substrate (MFIS) structured ferroelectric field effect transistor (FeFET), interfacial charge concentration, and charge migration rate under ionizing radiation. The capacitance and source-drain current at different total dose and different dose rate are calculated. Results show that the total dose of 0.1 MGy changes slightly the source leakage current and capacitance of the FeFET, and the total dose of 1 MGy leads to a larger variation in these quantities. When the radiation dose rate is varied, the minimal changes in the drain-source current and capacitance are observed. These results suggest that FeFET has a relatively large radiation hardness.