Through monitoring the temperature inside cryogenic equipment such as superconducting magnets, it is possible to detect indicators of failures and prevent equipment from becoming damaged. An optical fiber sensor is considered a suitable means of measuring the temperature inside cryogenic equipment because of its low heat invasion and high voltage insulating properties. In this study, we used a fiber Bragg grating (FBG) to investigate the reproducibility and multipoint measurement characteristics over a temperature gradient inside the cryogenic equipment. We also investigated the improvement of the wavelength shift change ratio at cryogenic temperature using a coated optical fiber sensor to enhance the thermal expansion coefficient.