Abstract: The transformer oil will release gas and even form suspended bubbles under the conditions of moisture, deterioration and decomposition. Under the coupling action of electromagnetic, thermal, flowing and other physical fields, the bubbles will show extremely complex electric fluid dynamics behavior, which will significantly affect the insulation performance of transformer oil. Therefore, it is of great significance to study the morphological evolution and motion law of bubbles in transformer oil. In this paper, a turbulent model is used to simulate the state of transformer oil flow, and a dynamic analysis model of suspended bubbles under multi-field coupling is constructed. The effects of interelectrode voltage, oil flow velocity, bubble size and bubble number on the coalescence behavior of suspended bubbles are studied, and the distribution characteristics of internal electric field during the evolution of bubble morphology are analyzed. The results show that the increase of interelectrode voltage and bubble size will delay the occurrence of bubble coalescence behavior. Once bubbles begin to coalesce and form a connector, the internal field strength will show a maximum value, which is positively correlated with interelectrode voltage and bubble size. The increase of oil flow velocity and bubble number will promote bubble coalescence in advance. The greater the oil flow velocity is, the greater the pressure gradient and deformation of the bubble will be, and the smaller the field strength inside the bubble connector will be, meanwhile, the increase of the number of bubbles will lead to the increase of the field strength inside the bubble connector.