This　paper　presents　a　novel　orthogonal　octo-rotor　Unmanned　Aerial　Vehicle　(UAV)　and　addresses　the　aerodynamics　of　the　UAV　with　varied　rotor　spacing　by　both　numerical　simulations　and　experiments.　Compared　with　the　traditional　planar　multirotor　UAV,　this　novel　orthogonal　octo-rotor　UAV　features　a　compact　structure　with　four　horizontal　main　rotors　for　stability　and　thrust　and　four　vertical　auxiliary　rotors　for　lateral　movement.　Additionally,　the　attitude　and　translation　dynamics　are　decoupled　with　easy　manipulations.　To　obtain　a　better　hover　performance,　the　flow　field　and　hover　performance　of　the　UAV　were　analyzed　with　rotor　spacing　ratios　i　=　D/L　ranging　from　0.55　to　0.9　(i　=　0.55,　0.59,　0.63,　0.67,　0.71,　0.77,　0.83,　0.90)　and　a　rotor　speed　ranging　from　1500　to　2300　RPM.　The　results　showed　that　a　rotor　spacing　ratio　of　i　=　0.55　achieves　a　better　hover　efficiency,　increasing　hover　efficiency　by　11.27%　at　2000　RPM,　where　the　maximal　thrust　increment　is　3.92%　and　the　power　consumption　decreased　by　5.68%　at　the　same　time.　Computational　Fluid　Dynamics　(CFD)　simulations　were　further　validated　by　streamlines　and　velocity　distributions.　It　indicated　that　the　rotor　interference　from　the　outflow　was　decreased　with　the　rotor　spacing　while　the　increasing　rotor　speed　aggravated　the　influence　of　the　auxiliary　rotor　on　the　downwash　airflow　of　the　main　rotor.　The　potential　benefit　of　the　rotor　interference　from　the　main　rotor　and　the　auxiliary　rotor　improved　the　hover　efficiency　of　the　orthogonal　octo-rotor　UAV　with　a　higher　thrust　increment,　which　offers　it　the　unique　capability　of　resisting　wind　gusts　or　even　rotor　failure,　which　will　be　validated　with　more　field　flight　tests.