Using　gas-state　reaction,　Nanometer　WO3　was　synthesized　by　gasstate　reaction　with　tungsten　filament,　WO3　mixed　with　TiO　2　made　by　Sol-gel　method　was　made　up　into　gas-sensor　to　H　2S.　The　gas-sensing　measurement　results　revealed　that　these　sensors　with　a　certain　sensitivity　put　into　H2S　gas　of　density　(about　10　-6)　and　present　good　response-recovery　characteristics.　By　analyzing　micro-structure　of　the　material,　the　mechanism　of　these　sensors　was　discussed.