The present study measures the lift and drag coefficients of airfoil NACA 0012 at ultra-low Reynolds number (Re=5 300) in an experiment. The investigation focuses on the free-stream turbulence intensity effect on airfoil lift coefficient and dray coefficient, and further explains this effect through a discussion of turbulence intensity influence on airfoil flow. The measured results indicate that, while airfoil stall does not occur in lift coefficient and drag coefficient for low turbulence intensity, it is clearly present for high turbulence intensity. For airfoil NACA 0012 and high turbulence intensity, the stall occurs at angles of attack from 12° to 15°. As demonstrated by the flow visualization around the airfoil, the influence of turbulence intensity is significant on both the airfoil boundary layer and the separated shear layer, so that the airfoil performance differs at different turbulence intensity. In addition, the influence of the increase of turbulence intensity and Re appears to be similar on the airfoil load characteristic and flow regime.