Abstract: The annealing characteristics under different conditions after 60 Co γ ray irradiation for rad hard 4007 NMOS transistor are explored, the irradiation sensitive parameters are investigated along with the radiation dose, annealing temperature and gate bias. The annealing velocity for 100 ℃ is higher than that for 25 ℃ at the same irradiation dose. The annealing degree of isochronal annealing is close to that of isothermal annealing at 100 ℃ for 168 h. The affection of gate bias in different annealing process is similar: the annealing rate for +5 V bias is faster than that for 0 V bias and float. The mechanism of oxide traps annealing and interface states increase as well as the tentative acceleration test method are discussed.