To　investigate　the　property　of　the　promising　and　eco-friendly　hydrogen-fueled　rotary　engine,　the　effect　of　excess　air　ratio　on　the　combustion　and　emission　characteristic　of　it　was　explored　by　experiment.　The　test　was　conducted　under　1500　rpm　and　5　CAD　ADTC　ignition　timing.　The　test　results　demonstrated　that　with　the　decrease　of　excess　air　ratio　from　2　to　0.85,　the　thermal　efficiency　of　the　hydrogen-fueled　rotary　engine　increases　first　and　then　decreases.　Besides,　increasing　MAP　is　beneficial　to　improve　thermal　efficiency.　Among　the　tested　condition,　the　highest　brake　thermal　efficiency　is　realized　when　the　rotary　engine　operates　at　1.4　excess　air　ratio　and　88　kPa　MAP,　about　18.34%.　And　the　excellent　HC　and　NO　emissions　can　be　obtained　at　the　highest　efficiency　point.　Besides,　with　the　decrease　of　excess　air　ratio　and　the　increase　of　load,　the　stability　and　flame　development　period　gradually　decrease.　With　a　decreased　excess　air　ratio,　the　flame　propagation　period　decrease　first　and　then　increases,　whereas　work　capacity　and　thermal　efficiency　increase　first　and　then　decrease.　For　NO　emission,　it　will　increase　sharply　near　the　equivalent　ratio　and　gradually　decrease　after　rich　combustion.　Also,　according　to　the　analytical　model,　it　is　found　that　the　power　performance　of　the　rotary　engine　depends　on　the　trade-off　relationship　of　in-cylinder　pressure　and　its　angle　of　action.　(c)　2021　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.