The　influence　of　different　film　thickness　on　grating　coupling　coefficient　and　transmittance　has　been　analyzed　based　on　a　four-layer　structure　model　of　grating　and　matrix　transformation,　in　which　the　optimum　thickness　of　coating　[(In2O3)9(SnO2)　1][indium　tin　oxide　(ITO)]　is　found,　and　the　influence　of　environmental　refractive　index　and　wavelength　for　the　effective　refractive　index　of　cladding　mode　is　simulated　in　theory,　respectively.　A　structure　of　long-period　fiber　grating　(LPFG)　coated　with　ITO　of　high-index　nanothin　film　by　the　pulsed　laser　deposition　technology　is　reported.　The　difference　of　refractive　index　sensitivity　of　LPFG　with　ITO　coating　or　not　is　analyzed　in　experiment.　The　refractive　index　sensitivity　of　LPFG　with　ITO　coating　or　not　is　-298　and　-150　nm/RIU,　respectively.　(C)　2019　Society　of　Photo-Optical　Instrumentation　Engineers　(SPIE)