The heat transfer characteristics of transformer oil natural convection in a cavity with a linear electrode were investigated by experiment and numerical simulation. The coupled physical and mathematical models of electric field, flow field and temperature field were established by the lattice Boltzmann method. The experimental results are in good agreement with the numerical simulation. In the absence of gravity, the enhancement effect of electric field on heat transfer is significant, and increases with the increase of voltage and heat flux. As to coupled convection caused by gravity and electric field force together, the electric field force destructs the natural convection caused by gravity, so applying an electric field at a low voltage will degrade heat transfer performance; as the voltage increases, heat transfer gradually becomes intensive, but the effect is limited. The study results revealed the enhancing mechanism of natural convection heat transfer under electric field and provided useful technical support for practical application. (C) 2017 Elsevier Ltd. All rights reserved.