Radiation effects of polycrystalline YBCO bulk sample irradiated by 60Co γ-rays from a dose of 1x106 up to 7.5×l09 rad at room temperature on critical temperature and critical current were investigated. IR spectrum was also used to study the mechanism of the irradiation. A considerable dependence of these parameters upon irradiation dose was observed. No significant effects on critical temperature were found, but the critical current in zero magnetic field changed greatly. It shows a tendency to decrease with the increase of the irradiation dose except for a slight increase with the dose less than about 2×107 rad and no simple relations between critical currents and irradiation doses was found. A typical case is that the critical current is reduced to about 60% when the dose reaches 5×109 rad, but the dependence of critical currents on magnetic field shows that the critical currents are higher than that of the unirradiated one in the range of magnetic field higher than 100 Gauss and decrease more slowly in magnetic field compared with the unirradiated one. The results indicate that the defects produced by γ-ray irradiation are benefit to flux pinning in higher fields. IR spectra analysis reveals that the intensity of the peak responsible for the Cul-O1 chain vibration is decreased, indicating that the bond of the Cul-O1 may be partly broken through collision process of the Compton electron produced by the γ-ray. This effect probably gives rise to decrease of the critical currents.