For the analysis of high lift system, a numerical method is presented, which is improved from Jacob``s method. From this analysis, lift and pitching moment can be obtained for multi-component airfoil system in incompressible flow. The applicability of the presented method is restricted to the field causing trailing edge separation. The potential flow calculation is based on singularity distributions (vortices and sources) on the airfoil surface. Separated flow region is simulated by outflow region, produced by source distribution on the separated part of airfoil surface. The separation point is predicted iteratively using computed results of potential flow calculation and boundary layer calculation for attached flow part. The comparison of the results of presented analysis and experiments for the airfoils of NACA 0010, NACA 2412 and NACA 4415 shows a comparatively good agreement.