This study focuses on the characteristics of low Reynolds number flow around airfoil of high-altitude unmanned aerial vehicles(HAUAVs) cruising at low speed.Numerical simulation on the flows around several representative airfoils is carried out to investigate the low Reynolds number flow.The water tunnel model tests further validate the accuracy and effectiveness of the numerical method.Then the effects of the relative thickness of airfoil on aerodynamic performance are explored, using the above numerical method, by simulating flows around airfoils of different relative thicknesses(12%, 14%, 16%, 18%), as well as different locations of the maximum relative thickness(x/c = 22%, 26%, 30%, 34%), at a low Reynolds number of 5 · 105.Results show that performance of airfoils at low Reynolds number is mainly affected by the laminar separation bubble.On the premise of good stall characteristics, the value of maximum relative thickness should be as small as possible, and the location of the maximum relative thickness ought to be closer to the trailing edge to obtain fine airfoil performance.The numerical method is feasible for the simulation of low Reynolds number flow.The study can help to provide a basis for the design of low Reynolds number airfoil. This study focuses on the characteristics of low Reynolds number flow around airfoil of high-altitude unmanned aerial vehicles (HAUAVs) cruising at low speed. Numerical simulation on the flows around low air. tunnel model tests further validate the accuracy and effectiveness of the numerical method. Chen the effects of the relative thickness of airfoil on aerodynamic performance are explored, using the above numerical method, by simulating flows around airfoils of different relative thicknesses (12%, 14% , 16%, 18%), as well as different locations of the maximum relative thickness (x / c = 22%, 26%, 30%, 34%), at a low Reynolds number of 1055. Results show that performance of airfoils at low Reynolds number is primarily affected by the laminar separation bubble. Of the premise of good stall characteristics, the value of maximum relative thickness should be as small as possible, and the location of the ma ximum relative thickness ought to be closer to the trailing edge to obtain fine airfoil performance. numerical method is feasible for the simulation of low Reynolds number flow. study can help to provide a basis for the design of low Reynolds number airfoil.