In order to obtain the long endurance advantage of unmanned aerial vehicles （UAVs） in performing special missions such as intelligence，surveillance，and reconnaissance，the diamond joined-wing configuration UAV has received great attention.At the same time，due to the high flight altitude and low flight speed，the flow has special flow phenomena such as laminar flow-separation-transition，and the flow is complex.Its aerodynamic characteristics was studied by numerical simulation in this paper.The research shows that the diamond joined-wing configuration UAV has good aerodynamic characteristics，but there is the interference between the front and after wings.As the distance between the front and after wings approaches，the more serious the air flow through the front wing is blocked，and the more serious the air flow through the after wing is downwashed.At the same time，at high angle of attack，the flow separation of the after wing is delayed due to the downwash flow，which moves the aerodynamic focus of the whole machine backward and increases the longitudinal static stability margin.