The aim of this paper is to study the unsteady aerodynamic interaction between a Krueger flap and a three-element airfoil using the finite volume method to solve the Unsteady Reynolds-Averaged Navier-Stokes equations. For a better understanding of this unsteady interaction, the Krueger flap is placed at different positions. Our results clearly show that the airfoil’s aerodynamic performance and the pressure distributions are strongly influenced by the Krueger flap position.