Corrosion resistance steels can be chosen and used as an alternative means of corrosion protection for cargo oil tanks (COTs) of crude oil tankers since the corrosion resistant steel performance standard (IMO MSC 289(87)) for corrosion protection for COTs of crude oil tankers was adopted by International Maritime Organization. The corrosion behavior of the conventional steel used as upper deck in COTs corrosion environment was greatly influenced by the lower and upper holding time at different temperatures. In this paper the different lower and upper holding time of conventional steel in simulated COTs corrosion environment was investigated. The corrosion mechanism in cargo oil tank environment with different lower and upper holding temperatures was studied by weight loss SEM EDX X-ray diffraction and electrochemical measurement. The results showed that with the increase of lower holding time of upper deck the radium of condensed water-dropthe content and the pH of condensed water presented different variations which directly decided the corrosion rate morphology and the composition of rust layers. But the upper deck temperatures holding time only led to the variation of the rust layer composition and had great effect on corrosion rate.