Abstract: Fabricated internal floating roof of aluinium-alloy have changed the conventional method of designing steel internal floating roofs (which look like floating pontoons). The structural characteristics are as follows: 1. Used as floating components are light aluminium-alloy floats, which have stable chemical properties and are not easily corroded; 2. Soft and anti-turning devices supported by fixed cables are adopted to prevent unbalancing ratial pressure state and wedging of the floating roofs; 3. Tonguing sealing belts can be adopted and installed on upper side of the floating roofs without contacting the oil surface, thus preventing the sealing belts from melting, being corroded, deforming, aging and being damaged so that the problem of poor sealing effects caused by the above mentioned factors can be completely solved. Recommended in the paper are tonguing fluororubber sealing belts, more effective if used in pure benzone and solvent oil tanks. The said internal floating roofs of aluminium-alloy have such advantages as being light in weight, convenient for installation and taking less time for reoperation, which helps saving the time it takes for reconstruction. Two light oil tanks are described in the paper as examples. The original internal floating roofs have been replaced by the fabricated ones made of aluminium-alloy. No accidents like leakage and sinking have ever accured so far after 4 year operation. In addition, they are very effective in energy saving and safety.