Micro　aerial　vehicles　(MAVs)　usually　suffer　from　several　challenges,　not　least　of　which　are　unsatisfactory　hover　efficiency　and　limited　fly　time.　This　paper　discusses　the　aerodynamic　characteristics　of　a　novel　Hex-rotor　MAV　with　a　coaxial　rotor　capable　of　providing　higher　thrust　in　a　compact　structure.　To　extend　the　endurance　during　hover,　flow　field　analysis　and　aerodynamic　performance　optimization　are　conducted　by　both　experiments　and　numerical　simulations　with　different　rotor　spacing　ratios　(i　=　0.56,　0.59,　0.63,　0.67,　0.71,　0.77,　0.83,　0.91).　The　measured　parameters　are　thrust,　power,　and　hover　efficiency　during　the　experiments.　Re-tip　ranged　from　0.7　x　10(5)　to　1.3　x　10(5)　is　also　studied　by　Spalart-Allmaras　simulations.　The　test　results　show　that　the　MAV　has　the　optimum　aerodynamic　performance　at　i　=　0.56　with　Re-tip　=　0.85　x　10(5).　Compared　to　the　MAV　with　i　=　0.98　for　Re-tip　=　0.85　x　10(5),　thrust　is　increased　by　5.18%　with　a　reduced　power　of　3.8%,　and　hover　efficiency　is　also　improved　by　12.14%.　The　simulated　results　indicate　a　weakness　in　inter-rotor　interference　with　the　increased　rotor　spacing.　Additionally,　the　enlarged　pressure　difference,　reduced　turbulence,　and　weakened　vortices　are　responsible　for　the　aerodynamic　improvement.　This　provides　an　alternative　method　for　increasing　the　MAV　fly　time　and　offers　inspiration　for　future　structural　design.