The mechanism of crack occurrence and propagation in optical fibers were reviewed with emphasis on the reliability of optical fibers. The lifetime prediction model of communication optical fibers were given on the basis of the fracture mechanics. The stresses distribution of optical fibers in the configuration of fiber coils was analyzed. A general model was derived for evaluating the mechanical reliability of this kind of coiled sensing fibers. The model was then simplified to an alternative model for engineering applications. This simplified model would bring the conserved results out rapidly and simply. Several numerical calculations of the failure probability in service time of various fiber coils with different fiber radius and bending radius were carried out using the simplified model. The results displayed the dependence of the failure probability on the parameters of the fibers, coils, and the process. According to the relation, the failure probability and the lifetimes could be estimated for fiber coils installed. Meanwhile, the relations provided the guidelines to various design solutions of the fiber coils with deferent geometric configurations and service conditions in the future.