This research focuses on the thin circular arc rotor airfoils at a low Reynolds number. A novel thin circular arc airfoil with a convex structure was designed in consideration of its demand for high aerodynamic performance, high structural strength, lightweighting and easy manufacture. A convex curve on the upper surface of the airfoil was adopted to increase the thickness of airfoil at the partial chord and a stiffener in the airfoil was installed to improve the structural strength of blade span wise. The designed thin circular arc airfoil has the maximum thickness of 4.3%, a circular average thickness of 2.5%, the maximum camber of 5.5% and an average camber of 4.5%. Numerical simulations for computing the aerodynamic performance of the airfoil were performed at the representative Reynolds number between 40, 000 and 100, 000, and the angle of attack (AOA) from -4°to 12° by using the two dimensional steady and incompressible Navier-Stoke equations. The pressure coefficient distribution line of airfoil surfaces and the velocity vector were acquired. A carbon fiber rotor with a diameter of 40 cm, a mass of 15 g and rotor pitch of 15.7 cm was manufactured with the present airfoil, and the experiments on the lift force and the structural strength in a hover state were performed and the results show the performance of the airfoil meets the use requirments. At present, the developed rotor airfoil has been successfully used in a rotor aircraft.