The earliest mullion windows are found in Han tombs and pottery houses, and brick and wood buildings and murals of the Tang, Song, Liao, and Jin dynasties are also widely displayed. Since the Ming Dynasty, it has been gradually replaced by sill windows in important buildings, but it is still used in folk buildings. Before the Tang Dynasty, there were still many mullion windows, which were fixed and could not be opened, so their functions and shapes were limited. Since the Song Dynasty, more and more windows were opened and closed, and there was a great development in the type and appearance. In the Song Dynasty, a large number of lattice windows were used. In addition to the square, there were ball patterns and ancient coin patterns, which improved the lighting conditions and increased the decorative effect. The sill window in the Song Dynasty has been applied to the sill wall between the two sides of the hall door. It is evolved from the lattice door, so the form is similar, but only the lattice eye, waist flower board and barrier free water board. The supporting windows were first seen in the Han pottery buildings unearthed in Guangzhou. The supporting windows in the north of the Qing Dynasty were also used on the sill wall. They can be divided into two parts. The upper part is supporting windows, and the lower part is picking windows, both of which have the same area. The southern buildings need more ventilation in summer. The area of the supporting windows is about twice that of the windows removed, and the patterns of the window panes are also very rich. The styles of doors and windows in the Ming and Qing dynasties basically inherited the practices of the Song Dynasty, and glass began to be applied to doors and windows in the middle of the Qing Dynasty. Chinese modern architectural doors and windows were developed in the 20th century. Metal doors and windows represented by steel doors and windows have a history of 90 years. The golden age for the development of doors and windows in contemporary architecture in China is 20 years from 1981 to 2001. In 1911, steel doors and windows were introduced into China, mainly from Britain, Belgium and Japan. In 1925, the national industry in Shanghai, China began to produce steel doors and windows in small quantities. Before the founding of New China, there were only more than 20 small workshops of handicraft industry. After the founding of New China, steel door and window enterprises in Shanghai, Beijing, Xi'an and other places have built large production bases for steel doors and windows, which have been widely used in industrial buildings and some civil projects. In the late 1970s, the state vigorously implemented the resource allocation policy of "replacing wood with steel", which set off a climax of promoting steel doors and windows, steel scaffolding, and steel formwork (referred to as "three steel replacing wood" for short), greatly promoting the development of steel doors and windows. The 1980s was the heyday of traditional steel doors and windows, with a market share of 70% (1989). Aluminum alloy doors and windows were introduced into China in the 1970s, but only used in foreign embassies in China and a few foreign-related projects. With the in-depth development of national economic governance and rectification and the achievement of results, the series of aluminum doors and windows has also developed from 4 varieties and 8 series in the early 1980s to more than 40 varieties and 200 series, forming a relatively developed aluminum door and window product system and establishing the status of pillar products.