In this study, an optical fiber temperature sensor based on up-conversion luminescence (UCL) is proposed. The core part is a new plan of the sensing unit, which is constructed with UCL materials of NaYF4: Yb3+, Er3+ nanocrystals by fiber fusion technology to achieve a wide range of temperature measurements. Experimental results show that the proposed optical fiber temperature sensor shows significant spectrum-temperature characteristics in 80-373 K temperature range. Its relative sensitivities at low temperature and normal temperature are 2.2×10-3/K with a determination coefficient of 0.957 and 9.1×10-3/K with a determination coefficient of 0.994, respectively. This type of sensor also has good mechanical strength and system stability and shows great potential for development, particularly in the aerospace field with large temperature differences.