In this study, the alumina coatings as tritium permeation barrier were deposited on 316L stainless steel by plasma electrolytic oxidation. The effects of plasma electrolytic oxidation on the coatings by different parameters were investigated, and the phase, surface morphology, thickness were characterized by XRD, SEM and eddy current method respectively. After analyzing through scratch adhesion test, thermal shock resistance test and tritium permeability test, it obtains the optimized coatings. The results show that phase, surface morphology, thickness are affected by current density, voltage and PEO (plasma electrolytic oxidation) duration time. The current density and voltage can change the phase structure of coatings, higher current density propel the transformation of Al→Al2O3 and higher voltage propel the transformation of γ- Al2O3→α-Al2O3.With increasing voltage and duration time, the pore size becomes bigger and the quantity is less so that surface morphology is worse. With current density increasing to appropriate state (9A/dm2), surface morphology is good. The coatings thickness increases with increasing density, voltage and duration time. After a series of tests, the coatings, which were obtained at 6A/dm2, 300V, 30min, has the good performance with film-substrate cohesion (86.0N) , thermal shock resistance( the coatings changed little after 280 times tests) and the tritium permeation resistance of coated sample is improved 3 orders of magnitude higher than the 316Lstainless steel bulk.