In order to analyze the main factors that affect the mechanical reliability and lifespan of optical fiber, through the simulating test conditions, the causes of optical fiber fracture are analyzed. The surface morphology of the experimental fiber fracture was compared with the morphology characteristics of the optical fiber fracture source that appeared in actual working conditions, and the main reasons for the formation of optical fiber fracture were qualitatively analyzed. Analysis suggests that the presence of water or vapor in the working environment under external stress accelerates the growth and propagation of surface cracks on the optical fiber, ultimately leading to fiber fracture.