In the present work, microstructural transformation of carbon nanotubes (CNTs) from the "herringbone" into highly crystalline structure in an electric field was experimentally observed by using a high-resolution transmission electron microscope and the growth mechanism was modeled and discussed by using a finite element method. It is found that the CNT microstructures can be changed by an electric field through the influence of the electrostatic force on the carbon surface and bulk diffusion on/in a deformed catalyst particle. Preliminary experiment revealed that an isomeric "graphite-nongraphite-graphite-nongraphite center dot" CNTs could be synthesized when a pulsed electric field is applied, which are expected to exhibit special properties and promising applications. (c) 2006 American Institute of Physics.