Abstract: In this paper, the transition from Cassie state to Wenzel state of water film at a hydrophobic surface with a nano-groove under the external electric field was studied by using molecular dynamics (MD) simulation method. It is found that there exists an optimal electric field strength, at which the transition of the wetting state can be promoted. For lower or higher electric field strength, it needs a longer time for the transition of the wetting state. Based on the calculation of the droplet contact angle under the electric field, it is found that the external electric field can enhance the surface wettability, which in turn facilitates the transition from the Cassie state to the Wenzel state. On the other hand, the elongation of the droplet along the electric field direction under the influence of the electric field polarization slows down the infiltration of the droplet into the nano-groove. Therefore, with the increase of electric field intensity, the transition time of liquid film wetting state shows a tendency of decreasing and then increasing after a minimum value. This paper reveals the mechanism of the transition of the wetting state on the surface of nanostructures under the influence of the external electric field, which contributes to a deeper understanding of the electrical wetting phenomenon on the surface with microstructures and nanostructures.