Experiments　were　carried　out　in　a　drop　tube　furnace　to　investigate　the　effects　of　biomass/coal　co-firing　and　air　staging　on　NO　emission　and　combustion　efficiency.　NO　and　CO　emissions　along　the　height　of　the　furnace　were　monitored　by　a　gas　analyzer,　and　the　content　of　unburned　carbon　(UBC)　in　fly　ash　was　also　tested.　Results　showed　that　NO　emission　from　straw　or　wood　combustion　only　account　for　1/3　or　1/2　that　from　coal　combustion,　respectively.　Under　the　conditions　of　biomass　co-firing,　the　increase　in　blending　ratio　had　a　positive　effect　on　the　reduction　of　NO　emission　and　combustion　efficiency.　Moreover,　results　of　air-staging　combustion　showed　that　for　coal　combustion,　air　staging　notably　reduced　NO　emission　and　combustion　efficiency.　For　biomass　combustion,　the　effect　was　slight.　Synergetic　analysis　indicated　that　there　was　an　optimum　biomass　co-firing　ratio　around　0.4,　when　the　positive　synergetic　effects　on　reducing　NO　emission　and　UBC　were　the　most　significant.　When　the　co-firing　ratio　exceeded　this　optimum　value,　further　increasing　the　co-firing　ratio　had　little　influence　on　NO　emission　and　combustion　efficiency.　After　air　staging　was　adopted,　the　degree　of　synergetic　effect　on　NO　emissions　was　reduced　while　that　of　UBC　was　increased.