Metallic conduction layer produced by the irradiation of the SrTiO3 surface is an intriguing phenomenon, where the process and mechanism of the insulating to conducting transition are still under debate. We have studied the influence of argon ion bombardment on the SrTiO3 (STO) single crystal by X-ray Photoelectron Spectroscopy (XPS) and Photoluminescence (PL). The former demonstrated the existence of a lower oxidation state of Ti, which implied oxygen vacancies were present at the near-surface region. The latter showed that the oxygen damage enhanced with increasing irradiation time, and decreased by annealing in oxygen at high temperature. The in-situ electrical conductance measurement during irradiation revealed the correlation between the resistance of ion-irradiated STO and the irradiation time. The existence of sufficient amount of oxygen vacancies was proposed to be responsible to the insulator to metal transition during the process of irradiation. (C) 2015 Elsevier B.V. All rights reserved.