H-beam is widely used in the construction in virtue of its excellent sectional properties. Because of its complex section, flange and web are deformed in different zones in rolling process. The traditional elongation ratio between flange and web is 1.03~1.05, which obtained from experience. Web wave, crack, or flange crack, and the large residual stress exist in the H-beam production. The problems are mainly caused by the uneven elongation of flange and web. It is necessary to keep uniform elongation of flange and web to solve these problems. The modified reduction ratio between flange and web is provided in this paper. The ratios improve the quality of H-beam by simulation and experiment.