The aerodynamic characteristics of the multi-element airfoil based on MS(1)-0313 airfoil were studied using CFD methods, obtaining the results of its lift coefficient, drag coefficient and pitching moment coefficient, as well as the effects of Reynolds number and relative width of flap gap on them. The results show that: the main wing provides most of the lift, the flap provides all of the drag, and the pitching moment of the main wing is slightly smaller than that of the flap; the boundary layer on the upper surface of flap separates at small angles of attack and gradually reattaches to the upper surface as the angle of attack increases. Through analysis of the flow field, it was concluded that both the Reynolds number and the relative width of flap gap influence the aerodynamic characteristics of the flap by affecting the flow characteristics in the gap, which in turn increase the circulation around the main wing and inhibit boundary layer separation on main wing's upper surface near trailing edge, thereby affecting the overall aerodynamic characteristics of the multi-element airfoil.