This study carried out a theoretical examination of the method of preparing very long unidirectional CNTs/resin composites by the application of an electric field. In the simulations, a rotating cylindrical multiple electrode was used to apply an electric field to the suspension (CNTs/uncured resin). The suspension was arranged closely under the rotating cylindrical multiple electrode, and moved slowly and perpendicularly to the axis of the rotation. The passing speed of the suspension was set to be (A) extremely slow compared with, or (B) synchronized to the circumferential speed of the rotating cylindrical multiple electrode. Condition (A) corresponds to a case in which the thinned suspension moves slowly under the rotating cylindrical multiple electrode at a high speed. In this condition, a DC voltage is applied to the electrodes. Condition (B) corresponds to the case that in which suspension is spread by the rotating cylindrical multiple electrode. In this condition, direct, four-phase square wave, six-phase square wave or eight-phase square wave voltages are applied to the electrodes in the simulation. The static electric fields in the suspension at many angles of the rotating cylindrical multiple electrode were calculated by FEM. Intensities of the obtained electric fields were assigned to the equations introduced by the author, and the CNTs alignment angle and the moment acting on the CNTs in the suspension were estimated. From the simulated results, it can be concluded that very long unidirectional CNTs/resin composites could be prepared by the application of an electric field.