GDS (Grating automatic Drawing System), which is an automatic design system of a metal product called grating, is a system that produces various detailed drawings on the basis of information within a Plan Drawing that represents layout of the grating such as locations, shapes, directions, etc. However, automatically produced drawings by GDS do not fully satisfy the standard of the general dimension marking method used among the layout designers. The lack of this standard quality mainly results from the fact that overlapping among dimension markings appear frequently. To solve the overlapping problem we applied the rule-based expert system. The rules are designed based on the expertise of skilled layout designers within the grating production lines.