In-situ and ex-situ oxide characterization was performed using synchrotron X-rays (SPring-8), to investigate the mechanism of stress corrosion cracking (SCC) of a non-sensitized cold worked 316 stainless steel specimen in high temperature water. The refreshed type auto-clave with two diamond windows was originally designed and fabricated to conduct the in-situ measurement in high temperature water using synchrotron X-rays. Chevron notched compact tension type specimens of a non-sensitized cold worked 316 stainless steel were loaded, exposed in simulated BWR water and analyzed using synchrotron X-rays under in-situ and ex-situ conditions. The oxide films and their layered structure near exposed surface were identified by X-rays diffraction and the local stress / strain beneath the oxide films were measured by X-rays diffraction. From these experimental results, the oxidation process for the non-sensitized cold worked 316 stainless steel in high temperature water was characterized, and a new model for the corrosion process of non-sensitized cold worked 316 stainless steel in high temperature water was proposed.