Continuing depletion of energy resources and concerns over secondary pollution have driven interests in dewatering and recovering oil from oily sludge generated in the numerous petroleum processing operations, such as production, transportation, storage, and refining. The high viscosity and emulsified water droplets in the sludge have significant impact on the dewatering efficiency and deoiling efficiency, as well as recovered oil quality. In this study, a combination process of demulsification, viscosity reduction, and centrifugation was proposed for dewatering and recovering oil from high-viscosity oily sludge. Based on its rheological properties, two solvents for viscosity reduction and three demulsifiers were examined. According to the degree of viscosity reduction, the naphtha named 120# solvent oil was selected as suitable solvent. The polyether demulsifier P9935 was identified in terms of its dewatering efficiency. Following the addition of the naphtha and demulsifier P9935, both centrifugation speed and centrifugation duration could significantly increase the deoiling efficiency and dewatering efficiency. There existed an optimum demulsification duration of 120 min to reduce the interfacial tension and thus increase the dewatering efficiency by 12.01%. The highest value of recovered oil quality and dewatering efficiency could be achieved at the demulsifier concentration of 0.3% with the increasing softness of asphaltenes films. As the dosage of demulsifier solution rose, the dewatering efficiency increased and the recovered oil quality became better. In general, the combination process is effective for dewatering and oil recovery from high-viscosity oily sludge.