A technique of relative optical interference intensity and a high-precision force measuring system are used to investigate the formation of ordered layer in the thin film lubrication by applying an external electric field (EEF). Experimental results indicate that the thickness of the lubricant film in a nanogap increases with EEF first, and then trends to a stable value. A strong EEF results in a high friction coefficient. When the electric power is turned off, the friction coefficient reduces again, but it cannot get back to that before the EEF was applied. The EEF effects on the film thickness and the friction coefficient are hardly related to the polarity of the EEF. The reasons for these experimental phenomena have been analyzed in the paper. (C) 2004 American Institute of Physics.