Interface forms between the embedded fiber and the composite. Cracks at the interface can initiate final damage. Therefore, the study of the interface between the embedded optical fiber and the matrix is of crucial importance. Single-fiber pull-out test was designed and used to study the formed interface. The value of the interfacial shear strength can be obtained by two ways. Studying the relationship between the embedded length of fiber and pull out force is one way. The other way is to find the critical length Lc, at which the fiber was broken instead of being pulled out. A low-range transducer was designed to precisely capture the magnitude of the pulling force. The force transducer was calibrated. It was shown that the output of force transducer was uninfluenced by the load position. The sensitivity of the transducer was 1.91 mV/V. Single-optical-fiber pull-out test results revealed that the coating of the fiber was broken at the boundary between embedded and bare parts, no matter how short it was embedded in the resin. The core and the clad of the optical fiber were pulled out from the coating, which was left inside the resin. Finite element analysis indicated that there was a region of stress concentration near the boundary at the coat. The shorter the embedded length was, the more intense the concentration was. However, the tests indicate that the coating of the optical fiber and the resin are in good imbibitions.