The reformation and characterization of the passive film formed on ultra-thin 316L after hydrogen charging was investigated by combining EBSD, TMDS, XRD, Synchrotron-based XPS, and electrochemical experiments. The results show that ultra-thin foil reforms a passive film after 12 hours of hydrogen release in NaCl solution. The reformed passive film was half the thickness of the as-received passive film and was dominated by Cr oxides/hydroxides. The lattice extension caused by residual hydrogen accelerated Cr migration to form Cr2O3; while the diffusible hydrogen occupied the cation vacancies and resulted in high defect density for the reformed passive film within 12 hours.