A fully depleted silicon-on-insulator (FDSOI) device is a promising structure for future ultrascaled devices because of its high radiation resistance. The buried oxide (BOX) layer of an FDSOI device not only enhances its robustness against single event effects (SEE) but also greatly reduces its ability to resist the effect of the total ionizing dose (TID). We studied factors such as the thickness of BOX layers and the bias state of FDSOI devices and proposed a 22 nm N-type FDSOI 2D device structure. The method of adding fixed charges to the BOX layer and adding state charges to the interface was used to simulate the TID effect. We showed that the thinner the BOX layer, the better the device’s ability to resist the effects of the TID. Increasing the total radiation dose causes the electron density of the channel to increase, indicating that the electron mobility of the channel is degraded. Because a large number of electrons are generated by irradiation, their density increases, causing a large number of electrons to collide with each other and scatter under a bias voltage, resulting in decreased electron mobility. By activating the built-in radiation model of the Sentaurus next-generation technology computer-aided design (TCAD) simulation tool, the device was used to simulate the TID effect under different doses in different bias states (OFF, ON, and transmission). The results showed that the most unappealing bias state of the TID effect for the short-channel N-type FDSOI device is the off state. This research provides new insights into the TID for FDSOI devices and can provide guidelines for future applications of radiation-hardened FDSOI-based circuits. The study of single particle effects plays an important role in the study of image sensors in space stations.