Abstract—A numerical simulation was performed using a vortex method in order to investigate the flow fluid to two tandem airfoils which arranged closer at variable angles of attack. Based on the shape of a vessel or a submarine, the mutual distance between the two airfoils (distance ratio) and the range of angle of attack were chosen. A symmetrical airfoil NACA0012 was used and the Reynolds number which based on chord length of airfoil c was Re = 3.8×105. The setting of distance ratio was L/c = 2.0 (here, L denote distance between two lift center of airfoil), the angle of attack of airfoils were varied as α = 0, ±5, ±10 and ±15 degrees. The initial stage was observed in this study. As a result of calculations, the flow pattern in each case was obtained, the variation of the fluid force in each case was investigated, and the variation of an overall lift coefficient was shown. By the mutual interference of two airfoils, it was found that the rapid variation of the overall lift coefficient occurs in an early stage.