Urbanization and real estate development are two mighty impetuses for the growth of China. An enhanced dynamic modeling has been devised to explore stocks and flows of buildings in the country and to quantify the related steel cycle. The uncertainties of the variables and results are investigated by the means of Monte Carlo method and sampling analysis. The building stocks are expected to increase to some 85–130 billion m2 in the mid-century, about 40–100% up from the current level. Throughout China but in urban areas in particular, concrete structures are replacing the buildings made of wood, clay brick, and primitive materials. By 2050 every two out of three buildings in China will be reinforced concrete- or steel-framed, leading to substantial demand for ferrous metals. Scenarios analysis shows that a slowing down in the building stock expansion will likely occur in China in no more than ten years. This may open up a transition with profound industrial and resource implications. Increasing businesses for the construction industry may emerge from maintenance, retrofitting, and end-of-life management of existing buildings. The steel industry shall reform its capacity to conform to the growingly available secondary resources and the declining requirement for construction steel. Efficient and appropriate recycling of steel content from waste concrete will play an important role in material conservation. A collaboration of improvements in process material efficiency with lifetime extension and application of high-strength steel may save nearly 40% of primary iron ores for building use in the coming four decades.