To　study　the　aerodynamic　performance　of　hovering　octorotor　small　unmanned　aerial　vehicles　(SUAV)　with　different　rotor　spacing,　the　computational　fluid　dynamics　(CFD)　method　is　applied　to　analyze　the　flow　field　of　an　octorotor　SUAV　in　detail.　In　addition,　an　experimental　platform　is　built　to　measure　the　thrust　and　power　of　the　rotors　with　rotor　spacing　ratios　L/D　of　1.0,　1.2,　1.4,　1.6,　and　1.8,　sequentially.　According　to　the　theory　of　momentum,　rotor　aerodynamic　performance　is　obtained　with　qualitative　analysis.　Further　analysis　with　numerical　simulation　is　presented　with　the　flow　field　of　the　octorotor　SUAV,　the　vorticity　distribution,　velocity　distribution,　pressure　distribution,　and　streamline.　The　results　show　that　the　aerodynamic　performance　varies　with　the　rotor　spacing.　Specifically,　the　aerodynamic　performance　is　poor　at　L/D　=　1.0,　which　is　accompanied　with　strong　interaction　of　wake　and　tip　vortexes　and　interaction　with　each　other.　However,　the　aerodynamic　efficiency　is　much　improved　with　a　larger　rotor　spacing,　especially　achieving　the　highest　at　L/D　=　1.8,　which　is　considered　to　be　the　best　rotor　spacing　ratio　for　this　kind　of　octorotor　SUAV.　©　2020　by　the　authors.　Licensee　MDPI,　Basel,　Switzerland.