Radiation effects of polycrystalline YBCO bulk sample irradiated by 6Β°C0 T-rays, dose of 1 Γ 106 up to 7.5 Γ 108 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 considerably strong dependence of these parameters upon the irradiation dose was observed. No significant effects on the 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 X 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 X 109 rad, but the dependence of critical currents on the magnetic field shows that the critical currents are higher than those of the unirradiated one in the range of magnetic field higher than 100 G and decrease more slowly in a magnetic field compared with the unirradiated one. The results indicate that the defects produced by T-ray irradiation are beneficial to flux pinning in higher fields. IR spectra analysis reveals that the intensity of the peak responsible for the Cu( 1 )-O( 1 ) chain vibration is decreased, indicating that the bond of the Cu( 1 )-O( 1 ) may be partly broken through collision process of the Cornpton electron produced by the T-ray. This effect probably gives rise to a decrease of the critical currents.