In　this　paper　the　premixed　catalytic　combustion　emissions　such　as　CO,　unburned　hydrocarbon　(UHC),　NOx　and　the　temperature　distribution　in　the　catalytic　monolith　with　ultra　low　concentration　of　Pd　were　studied.　Three　types　of　monoliths　were　used　for　experiments　and　the　temperature　of　preheated　air　was　respectively　50　degrees　C,　100　degrees　C　and　200　degrees　C.　The　results　showed　that　preheated　air　made　radial　temperature　in　the　catalytic　monolith　uniform　which　helped　to　avoid　local　hot　spots　so　as　to　decrease　NOx　emission.　The　experiment　also　proved　that　the　shorter　monolith　showed　much　better　catalytic　combustion　performance　than　longer　one　and　the　temperature　at　the　exit　of　the　shorter　monolith　was　relatively　lower.　On　the　contrary,　the　temperature　was　higher　in　the　longer　monolith　and　the　lethal　NOx　emission　was　slightly　increased.