Electrospinning technique has been recognized as an efficient method to manufacture nano-fiber. At present, research focuses on the structure and morphology of the fibers, a few investigations have been reported the mechanism of electrospinning. In our experiment, appropriate polymer EVOH (ethylene/vinyl alcohol copolymer) and different solvents were chosen, the energy change in the process of molecule orientation was analyzed by computer simulation, and the morphologies of the fiber were indicated by scanning electron microscope (SEM). Results indicate that: in the process of molecule orientation, some barriers should be overcome; the height of the barrier is determined by the relaxation times (T) of the molecule. The relaxation times vary in different solutions, when the relaxation time is short, the orientation of molecule is easy, so jet instability will be fierce, and fibers with small diameter are obtained. (c) 2005 Elsevier Ltd. All rights reserved.