Abstract: The effect of aspect ratio on the aerodynamic characteristics for a 15 cm fixed-wing microaircraft airfoil was studied. Based on the common airfoil shape of the MAV, the four kinds of aspect ratios were set. The finite volume method was used to numerically simulate the three-dimensional flow around different aspect ratio models, and the surface flow field on the model and the influence of the flow around the wing tip on the flow field of the upper and lower surfaces were analyzed. It is concluded that when the aspect ratio is 0.5, the pressure difference between the upper and lower surfaces is small, and the lift is insufficient; when the aspect ratio is 2, the upper airfoil surface will have a large airflow separation in the common attack angle range; when the aspect ratio is 1, the lift surface is greatly affected by the wing tip vortex; The fixed-wing MAVS with aspect ratio of 1.5 can not only maintain high lift force with big aspect ratio, but also avoid the adverse effects of airflow separation at high angle of attack. This research has certain guiding significance for MAV design.