The　light　propagations　in　human　lung　and　three-layer　tissues　of　artery　are　simulated　by　Monte　Carlo　method.　It　results　that,　with　the　increasing　of　the　refractive　index,　the　diffuse　reflectance　Rd　is　linearly　decreased　and　absorptance　A　is　almost　linearly　increased.　But　for　multi-layer　tissues,　the　influence　of　the　refractive　index　in　the　deeper　layer　of　the　tissue　on　Rd　is　less,　and　the　influence　of　the　refractive　index　in　the　different　layer　of　the　tissue　on　A　is　different　because　each　layer　has　its　own　thickness　and　optical　property.　Therefore,　the　refractive　index　is　a　very　important　parameter　in　bio-tissue.