Abstract: The interface problem of composite materials has some particularity, complexity and importance. It not only is related to the processing of materials, but also has a prominent effect on the damage and failure process. In this paper, the micro deformation of a single fiber in the single fiber/epoxy composites is measured by using the laser Raman spectroscopy (LRS) technique and the micromechanics of stress transfer is investigated. From the experiment, it can be found that the average strain in fiber increases linearly with the applied strain up to 0.8%, at which the fiber occurs to fracture.