A　highly　birefringent　photonic　crystal　fiber　loop　mirror　temperature　sensor　based　on　Sagnac　interferometer　structure　is　designed.　As　the　photonic　crystal　fiber　has　good　temperature　stability,　in　order　to　achieve　the　temperature　sensing,　ethanol　which　has　a　high　thermal　coefficient　is　filled　into　the　air　holes　of　the　high　birefringence　photonic　crystal　fiber.　Using　plane　wave　expansion　method,　the　relationship　between　birefringence　of　the　highly　birefringent　photonic　crystal　fiber　and　transmission　wavelength,　and　that　between　birefringence　and　temperature　are　analyzed.　Theoretical　analysis　shows　that:　filled　with　ethanol,　the　birefringence　of　high　birefringence　photonic　crystal　fiber　increases　with　the　increase　of　the　transmission　wavelength　and　temperature,　besides,　there　is　a　linear　relationship　between　birefringence　and　temperature.　In　the　experiment,　a　piece　of　high　birefringence　photonic　crystal　fiber　filled　with　ethanol　is　welded　with　a　3　dB　coupler　to　form　a　fiber　loop　mirror.　When　the　temperature　rises　from　45　°C　to　80　°C,　the　concave　point　drift　of　309.280　nm　towards　the　short　wavelength　is　observed　on　spectrum　analyzer.　The　sensitivity　is　as　high　as　8.837　nm/°C.