The demulsification and dewatering treatments of emulsion are the critical link in the recycling technologies of industrial waste oil. A device coupled with centrifugal and high-voltage fields were proposed for the emulsion with a high content and a complicated composition, which cannot be achieved using a single method. Combining with the governing equations of flow field, electric field and droplet size, the numerical simulation model of the coupling device was established. The functional relationship between structural parameters and separation efficiency was further determined by response surface methodology. From this the structural optimization of the device was achieved and the influence of embedding a high-voltage field on structural optimization was examined. Results show that the response models can reasonable optimize the structure of coupling device and predict its separation efficiency. In comparison to the numerical results, the maximum deviations of the dewatering and deoiling rate models are about 0.8% and 3.7%. Embedding a high-voltage field does not influence the selection of optimal range under the single-factor conditions, but affects the multi-parameter optimization design of the coupling device. Specially, the influence of the interaction between the variables on separation efficiency changes when the electric field is applied and varied. In addition, at 11 kV, the dewatering and deoiling rates reach up to 95.8% and 96.8% when the optimal values of the nominal diameter and the large and small cone angles are 22 mm, 20.0 degrees and 5.1 degrees. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.