The key results of multiple saturation output characterization campaigns of charge coupled device(CCD) were presented. These characterizations encompassed proton, neutron and cobalt-60 irradiation tests at room temperature and annealing. This gives us the opportunity to discuss differences and similarities on CCDs of degradation of saturation output induced by proton, neutron and cobalt-60 radiation. The experiments show that the saturation output is degraded markedly induced by total ionizing dose, degradations of saturation output at different total dose and the recovery after annealing were compared, while no obvious degradation after neutron irradiation(neutron irradiation only induced displacement damage). Mechanisms for these saturation output changes were discussed, saturated output degradation mainly caused by threshold voltage decreases of irradiation, resulting in full-well capacity decline. In addition, the gain of the output amplifier was decreased by total ionizing dose. Further insight on the underlying physical mechanisms could be gained by simulating the charged particle track influence on the pixel electric fields, along with the diffusion, drift, and recombination processes that occur between charge generation and collection.