In response to the fiber optic circuit failure of Nanrui Optical CT at Lingzhou Station, the fiber optic status is analyzed by OTDR technology and the failure point is successfully located. Through on-site inspection, it is found that the fault is caused by icing of the penetrating tube, which results in increased attenuation of the fiber optic cable after being squeezed. Then, in order to investigate the failure and consequences caused by icing through the pipe, the low-temperature icing experiments on four kinds of optical fibers are conducted. It is found that the 4-core fiber optic cables（GYPFJS-4B1）provided by YOFC and the 6-core fiber optic cables with center tube（GYMXTW-48B1.3）provided by Fiberhome have insignificant changes in average attenuation in the process of temperature change, and they have a good fiber optic and fiber optic cable structural design. It can satisfy the requirements of pipe laying in a low-temperature environment, and provide a data basis for improving the reliability of the optical CTs in low-temperature environment applications.