Small size of steel reinforced concrete beam was prepared. Cracks have been induced by three point bending test. Through wetting drying cycles with NaCl solution, the corrosion of reinforcing steel in the RC beam has been accelerated. The corrosion potential of the carbon steel reinforcement has been measured by using the natural potential method. The corrosion product distributions on the steel surface have been analyzed by means of neutron tomography. Results obtained indicate that after 85 wetting drying cycles, the reinforced concrete beam can be scanned in three dimensions by the technique of neutron tomography. The spatial distributions of corrosion products around the steel reinforcement in the RC specimen can be visualized directly. The corrosion products are mainly concentrated at the interfaces between steel reinforcement and mortar matrix along the crack section. The corrosion products may gradually develop outwards along the steel at the interfaces. This phenomenon is in accord with the mechanism of pitting corrosion induced by chloride ions. A new experimental approach to study the corrosion mechanism of steel in reinforced concrete structures is provided.