Abstract: Cleaning of crude oil tank includes equipment installation, oil/water washing, artificial slag removal and equipment removal. Installation and removal of cleaning equipment and oil/water washing process should be enhanced to improve the cleaning efficiency. In this regard, the modularized equipment, namely the valves and pipe fittings made into module which can be installed and removed as a whole, is applied to shorten the time required for installation and removal. Moreover, oil/water washing processes is optimized to increase the cleaning pressure at tank top and regulate the supply of cleaning oil and recovery of crude oil, which helps to reduce the cleaning time. The case study shows that unnecessary cleaning time is reduced through optimization and the efficiency of equipment is improved, while the cleaning effect is ensured.