Discharging the wastewater from ship washing directly will pollute the environment, so it has to be processed before discharging, among which the treatment of oily wastewater is an important and difficult task. The high COD oily wastewater from a Chongqing company’s ship washing center under the most unfavorable condition was taken as the research object, which was treated by the combined process of coagulation demulsification and Fenton oxidation. During the coagulation demulsification process, the type, dosage, pH value and stirring time of the coagulants were analyzed, suitable conditions in the Fenton oxidation process were also determined, including H2O2 concentration, Fe2+ concentration and reaction time. Then the optimal conditions for oily wastewater pretreatment were determined through orthogonal experiments. The results show that PAC is a suitable inorganic coagulant, and the suitable dosage for the coagulation demulsification process is 75 mg/L, the initial pH value is 8, and the stirring time is 3 min. The suitable H2O2 and Fe2+ concentration for Fenton oxidation is 12, 500 mg/L and 1, 250 mg/L respectively, while the reaction time is 120 min. Under optimal conditions, the total COD removal rate of the experimental water samples can reach 70%, in addition, TP and petroleum are almost completely removed. This work provides a theoretical guidance for the engineering design and commissioning of the ship washing wastewater pretreatment project at a certain port of the Yangtze River.