Monte　Carlo　method　is　used　to　simulate　light　distribution　in　human　artery　of　three　layers　that　is　irradiated　respectively　by　two　different　surface　photon　sources　(Guassian　beam　and　flat　beam)　of　0.06cm　radii　at　wavelength　of　633nm.　Fluence,　diffuse　reflectance　and　diffuse　transmission　distribution　of　the　tissue　are　given　when　the　two　surface　photon　sources　illuminate　the　tissue　respectively.　The　influence　of　the　shape　of　the　incident　beam　on　the　above　parameters,　and　that　of　the　refractive　index　n　on　the　diffuse　reflectance　Rd　and　absorptance　A　of　the　tissue,　are　discussed.　The　obtained　results　are　:　the　diffuse　reflectance　Rd　and　fluence　Phi　are　mainly　distributed　in　radial　scale　of　the　size　of　the　incident　beam,　and　the　influence　of　the　shape　of　the　incidence　beam　on　the　radial　distribution　of　Rd　and　Phi　is　also　in　the　scale　of　the　size　of　the　incident　beam,　whereas　that　of　the　shape　of　the　incident　light　beam　on　the　diffuse　transmission　is　little.　Rd　is　linearly　decreased　with　the　increasing　of　n　in　each　layer　tissue,　but　the　influence　of　n　in　deeper　layer　tissue　on　Rd　is　little;　absorptance　is　linearly　increased　with　the　increasing　of　n　in　each　layer　tissue.　Therefore,　the　refractive　index　is　a　very　important　parameter　in　biotissue.