Abstract: Factors impacting on evaporation loss of light gas for large-scale steel floating roof oil tank are analyzed.Aiming at the issue arising from poor sealing between floating roof and tank wall, measures for improving surface roughness over tank inner wall by adopting coating preparation are put forward.Rehabilitation practice for floating roof tank demonstrates that the surface friction coefficient of the inner wall reduced greatly after coating rehabilitation, over 90% is decrease for surface oil, oil loss in unloading is only 3.1% compared with that prior to rehabilitation and turnover loss is reduced to 62.7%.