Because　of　the　characteristic　of　wavelength　encoding,　fiber　Bragg　grating　(FBG)　has　the　advantages　of　immunity　to　light　power　fluctuation,　variation　in　polarization　and　connecting　loss,　so　it　has　high　sensing　precision.　However,　for　the　demodulation　of　FBG,　wavelength　signal　is　usually　converted　to　electric　amplitude　signal.　By　measuring　the　amplitude　signal,　the　sensing　result　is　obtained.　It　is　well　know　that　the　amplitude　signal　is　easy　to　be　disturbed　in　sense.　For　this　reason,　amplitude　demodulation　limits　the　effect　of　wavelength　encoding　of　FBG.　This　paper　presents　a　novel　method　of　counting　wavelength　demodulation　for　FBG　sensors　using　a　high　birefringent　fiber　(HBF)　loop　mirror.　This　demodulator　has　simple　structure,　high　precision,　low　cost　and　convenient　to　use.　The　resolution　of　the　loop　mirror　device　with　30　meter　long　of　HBF　is　0.067　nm.　This　counting　wavelength　demodulating　method　has　the　significance　for　widespread　practical　application　of　FBG　sensors.