Eu　doped　ZnO　thin　films　were　deposited　on　a　Si(100)　substrate　using　a　spraying　pyrolysis　method.　The　precursor　solution　was　sprayed　by　N-2　carrier　gas.　To　form　polycrystalline　ZnO　material,　the　substrates　were　set　into　a　tube　furnace　to　maintain　the　deposition　temperature　at　350　degrees　C.　Using　a　Rutherford　backscattering　(RBS)　system,　the　atom　distribution　of　elements　between　the　ZnO:Eu　thin　films　and　Si(100)　substrates　was　examined.　The　experiments　show　that　the　transition　layers　exist　between　ZnO　thin　films　and　the　Si　(100)　substrate.　The　RBS　measurements　and　simulation　reveal　that　the　formation　of　the　layer　is　controlled　by　the　diffusion　of　Si　into　the　ZnO　thin　films.　This　fact　indicates　that　the　diffusion　of　Si　into　oxide　thin　films　should　not　be　neglected,　even　at　low　temperature　of　350　degrees　C.　By　applying　the　Fick＇s　Diffusion　Law,　the　diffusion　capability　of　Si　into　ZnO　thin　films　with　different　Eu3(+)　doping　was　studied　and　calculated.　It　is　concluded　that　the　doping　Eu3+　will　strongly　hinder　the　diffusion　of　Si　into　ZnO　films　due　to　the　precipitation　of　Eu3+　at　the　grain　boundary.