Gas flow over a flat-plate airfoil at very-low Reynolds number is investigated in order to understand the aerodynamic issues related to micro air vehicle design and performance. Studies have shown that such low Reynolds number flow exhibits rarefied phenomena and a flat plate having a thickness ratio of 5% has better aerodynamic performance than conventional streamlined airfoils. This paper simulates air flows over a 5% flat plate using a hybrid continuum–particle approach for flows having a Mach number of 0.2 and a Reynolds number varying between 1 and 200. Investigation shows that low Reynolds number flows are viscous and compressible, and rarefied effects increase when the Reynolds number decreases. It is also found that there is a minimum lift slope for the plate airfoil at a Reynolds number near 10 and the drag coefficient monotonically increases with decreasing Reynolds number.