The proton and neutron irradiation and annealing experiments are carried out on a domestic buried channel CCD (charge-coupled devices), Monte Carlo method being applied to calculate the energy deposition of scientific CCD irradiated by proton and neutron, and the radiation damage mechanism of the device is analyzed. The displacement damage dose in N+ buried channel is simulated. During irradiation and annealing experiments, the main parameter (dark signal) is investigated. Results show that the dark signal of the buried channel CCD irradiated by 10 MeV proton and 1 MeV neutron rises obviously. With the same fluence, the increase of dark signal and the displacement damage dose in N+ buried channel caused by 10 MeV proton is larger than that by 1 MeV neutron. Dark signal caused by proton irradiation is divided into surface dark signal and bulk dark signal. Oxide-trapped-charges and interface states may be caused by ionization-generated surface dark signal, and the bulk defects may be caused by displacement-generated bulk dark signal. Neutron irradiation only affects the bulk dark signal. Defects and their annealing temperature are studied. The dark signal of CCD irradiated by proton is greatly reduced after annealing, this phenomenon means that the dark signal is mainly affected by ionization. The proportion of bulk dark signals in total dark signals can be calculated by the remainder of dark signal after annealing, and it is at most about 20% or less. From the formula, the position of energy level of bulk defects has an obvious influence on the bulk dark signal. The energy level in the middle of the forbidden band can provide effective hot carriers. Combining the results of experiment and simulation, when the displacement damage doses in N+ buried channel are the same, the bulk dark signal produced by proton is nearly the same as that produced by neutron. This phenomenon means that the defect levels in the forbidden band gap caused by proton and neutron irradiation have the same contributions to dark signal generation. Effect of proton and neutron irradiation on the bulk dark signal is homogeneous. The displacement damage dose can be used to characterize the degradation degree of the bulk dark signal in CCD after irradiation.