A drop of water subjected to a pulsed electric field in emulsified oil undergoes periodic stretching vibration, which is very effective for promoting the coalescence of the emulsified drops. In this study, the forces that act on a single water drop during its vibration in a pulsed electric field are analysed, and a dynamics model of the vibration of the drop is developed. The expression of the model indicates that the vibration can be described as a non-linear parametric excitation vibration, and comparison of the model predictions with experimental results reveals a good similarity. In addition, a first-order approximation of the predictions of the model is used to obtain the waveforms of the vibration, and the peak of the amplitude-frequency curve reveals the occurrence of resonance. This affords a basis for determining the optimal demulsification frequency of the emulsified oil in the pulsed electric field. (C) 2015 Elsevier Ltd. All rights reserved.