Abstract: This paper mainly studies the influence of content and orientation of fibers upon the electrical properties of unidirctional glass fiber reinforced epoxy resin composites.The results indicate that the change of fiber orientation and the direction of applied electric field results in the change of breakdown strength,and the bigger the angle between fiber orienration and direction of electric field is,the higher the breakdown strength. The electrical properties of unidirectional fiber laminted plate decrease with the increase of fiber content.This paper establishes a submicroscopical dielec1ric model of unidirectional fiber composite,and on the basis of this model,the relationship between the breakdown intensity or electrical constant with the fiber content and orientation was theoretically predicated,the results between experiment and theory show a good agreement.