The total ionizing dose effect of 22 nm bulk silicon nFinFET was investigated by 60Co γ irradiation experiment. The variation of total dose radiation damage with irradiation bias and device structure was obtained, and the damage mechanism was revealed. The experimental results show that the threshold voltage of the device shift positively after ON bias irradiation, while the threshold voltage of the device shift negatively after TG and OFF bias irradiation. The threshold voltage degradation of the device with fewer fin number is greater than that of device with more fin number. By analyzing the action process of trap charge induced by irradiation, the reason for the above experimental phenomenon is revealed.