Remote　and　accurate　temperature　measurements　in　severe　environments　are　of　great　importance.　A　1525-nm　wavelength　located　in　the　C　band　of　optical　fiber　communication　is　used　as　a　pumping　light　source　for　NaYF4:Er3+　phosphor　possessing　high　upconversion　efficiency.　The　upconversion　luminescence　characteristics　were　demonstrated　in　the　temperature　range　of　160-400　K.　Based　on　the　thermal　coupling　energy　level　theory,　the　temperature　measurement　principle　of　the　fluorescence　intensity　ratio　is　analyzed.　The　energy　gap　between　the　2H11/2　and　4S3/2　energy　levels　of　the　Er3+　ions　is　approximately　787　cm−1,　which　is　appropriate　for　a　temperature　sensor.　The　experimental　results　indicated　that　its　maximum　temperature　sensitivity　was　0.00335　K−1.　The　proposed　optical　fiber　temperature　sensor　indicates　good　hysteresis　and　repeatability　and　has　potential　applications　in　resisting　electromagnetic　interference　and　remote　temperature　sensing.　©　2021　Optical　Society　of　America