Abstract: Mechanical washing technology for large vertical oil storage tanks has been gradually popularized in China. At present, China's mechanical cleaning sector is basically monopolized by the COW system. Some foreign mechanical cleaning systems (e.g. COW, BLABO, and COS) and their application in China are introduced in this paper. The research work dedicated to mechanical cleaning system in independent research and development process in China is described. It is pointed out that the existing COW-based cleaning system objectively exists poor adaptability of cleaning gun to different cans, non-compliance of oily wastewater disposal and treatment and other outstanding issues; effective ways are put forward to solve the issues through adopting mobile cleaning robot, cyclone flotation integrated degrease technology to achieve high efficiency and environmental protection for large vertical storage tanks mechanical cleaning operations.