In this study, the alumina coatings as tritium permeation barrier were successfully prepared on stainless steel bulk by composite low temperature plasma method of magnetron sputtering, heat treatment and O ion implantation. The phases, surface morphologies, chemical composition and O distribution of the coatings were characterized by XRD, SEM, EDS and AES individually,and after analyzing through scratch adhesion test, thermal shock resistance test and tritium permeability test. The results show that the Al coatings deposited by magnetron sputtering is well, and Fe-Al alloys interlayer was formed after heat treatment. In O ion implantation process, the oxygen depth deepened and the oxygen density gradient decreased with higher accelerating voltage at definite doses, meanwhile it can be seen that 8×10₁₇ ions/cm₂ is the crucial dose, above which ion implantation the oxygen density was more homogeneous. After a series tests, the obtained coatings has the good performance with film-substrate cohesion, thermal shock resistance and the tritium permeation resistance, and the coatings, which were treated by superposition at 8×10₁₇ ions/cm₂doses, have the best tritium permeability resistance, and it was improved 3 orders of magnitude high than the stainless steel bulk.