Cleaning of sewage tanks in chemical plants has always been a high-risk operation in confined spaces. In the past, personnel entered the tanks for cleaning. The site smelled seriously, and the organic hydrocarbon content often exceeded the standard. Personnel suffocation, poisoning, and fire and explosion accidents are prone to occur during the cleaning. The control of the cleaning process has always been a difficulty point. In order to prevent accidents, an advanced mechanical cleaning technology was introduced from the perspective of personal safety, health and environmental protection. It was applied in the cleaning of sewage tank for the first time, and good results were achieved.