This paper presents a modeling algorithm that helps automatically generate a quadrangulation strip for flank milling which minimize the cutting error to a designed reference surface. Two curves are given as the boundary of a ruled surface to be machined. We discrete two curves into sample points and try to connect them to form quadrangles by rule lines, where these rule lines simulate the cutter's moving trajectory (i.e. tool path). Not only the surface error but also some other engineering constraints are considered in our optimal quadrangulation algorithm.