Abstract: Oxidation behaviors of steel Super 304H in water vapour atmosphere at 650 ℃/25 MPa were studied under six surface conditions, i.e. with sample surfaces respectively treated by coarse grinder, grin-ding wheel, abrasive paper grits 320, 600 and 1200, and with polished surface, during which the samples after 1 200 h oxidation were weighted using gravimetric method, while the morphology and microstructure of oxide layers analyzed by SEM and EDS, and corresponding phases characterized by XRD. Results show that the steam oxidation resistance of steel Super 304H is relatively sensitive to the surface state of samples; different surface state results in different mass variation, oxide morphology and microstructure of samples; the typical oxide films generally consist of two layers, the outer layer is mainly Fe₃O₄, while the inner layer mainly Cr-rich (Fe,Cr)₃O₄ with a small amount of Cr₂O₃. Protective Cr-rich oxide films are easy to form on surfaces of lower finish with strained layer, when better steam oxidation resistance is to be generated.