Studying the surface characteristics of ultra-thin stainless steel substrate helps to understand and analyze the contact and material removal mechanism during its chemical mechanical polishing(CMP).The organizational structure, surface morphology, surface roughness, surface defects, mechanical properties, and so on, were studied with the SEM, OLS4000 laser confocal microscope, Mahr Surf XR20 surface profiler, etc. The results of measurement and calculation show that the SUS304 ultra-thin stainless steel's surface defects usually were depressions, wrinkles, rust, scratches, stuttering and hemp points, wits thickness error is only 0.4%, the actual density is less than the theoretical density, its original surface geometric roughness is 28.5 nm, the original surface of the root mean square roughness is 62.18 nm, the original surface's contour deviates from the average line' arithmetic mean is 38.55 μm.