Abstract: Oilfield sump oils are mainly composed of oil recovered in well site, tank heels and floating oil from plant of water disposal. They get degraded during long time exposure to oxygen, and are characterized by high content of water and sand and stable emulsification conditions. In addition, the natural emulsifiers in the sump oil, such as gum, asphaltene and naphthenic acid, get enriched on oil- water contact, resulting in a strong interface membrane, therefore it is very difficult to treat them with conventional demuldifier and three - phase dehydrator. Laboratory study shows that the sump oil treating chemical JH002A and JH002B and sinking agent JH001B that we developed can effectively treat oilfield sump oil under optimum treatment conditions and with thermal chemical methods. Field experiment also proves that the treatment technology and treating agents can successfully and effectively treat oilfield sump oil and have strong practicability and large values of deployment.