Through analyzing the development stage of iron and steel industry, fitting the output curve of crude steel in the United States and Japan, the paper can summarize the law of development of iron and steel industry, and verify the feasibility of industry life-cycle theory. Now the iron and steel industry in China is passing the growth stage to maturation stage, using the industry life-cycle curve, the paper finally gets that the crude steel output of China is expected to reach saturation in 2020, and the saturation volume is about 770 to 850 million tons.