Ionizing radiation effects of typical clock oscillator and its internal oscillator circuit SM5009 for satellite was studied by ^60Coγ-rays in this thesis. Output signal amplitude and supply current of clock oscillator were measured under irradiation conditions. Relationship between the change of these parameters and the failure of SM5009 oscillator circuit was also analyzed. The results showed that the field oxygen parasitic leakage of SM5009 was very severe under irradiation, and the leakage current could increase to 10-4 A when the absorbed dose accumulated to 1500 Gy（Si）. It was a significant reason that caused the supply current of clock oscillator increase. Meanwhile the high level of output voltage was sensitive to absorbed dose for SM5009. The high level of output voltage decreased for 0.5 V when the absorbed dose accumulated to 1500 Gy（Si）. This was an important reason that caused the output signal amplitude of clock oscillator decrease.