In this paper, supercritical carbonation tests of steel fiber reinforced concrete (SFRC) are carried out. The effects of volume fraction and length-diameter ratio of steel fiber on the carbonation depth of SFRC under supercritical conditions are studied. A novel multi-phase and multi-physics coupling model for supercritical carbonation of SFRC is proposed, which considers random distribution of coarse aggregate, porosity, and steel fibers in SFRC, as well as the distribution of interfacial transition zones (ITZ) between coarse aggregate, steel fibers and cement. The results indicate that the porosity of the SFRC is reduced by 32.3 %, and its compressive strength of SFRC increases by 25.1 % ∼ 42.7 % after supercritical carbonation treatment. When the volume fraction of steel fiber is less than 1.5 %, the supercritical carbonation depth of the SFRC decreases with the increase of the volume fraction and the length to diameter ratio, respectively. The influence of the ITZ between coarse aggregate and cementitious matrix on the supercritical carbonation depth of the SFRC is found to be 2 to 6.8 times greater than that of the ITZ between steel fibers and cementitious matrix. The average carbonation depth of the SFRC increases gradually with the increase of ITZ thickness and porosity. The effect of ITZ porosity on the supercritical carbonation depth of the SFRC is more significant than that of ITZ thickness.