The Wunu Mountain city is capital of Gaogouli (Koguryo) built by Zhu Meng who was the first king (37 BC – 3 AD) in Huanren county, Liaoning province. The nature and technics of ironware and the development level of the handicraft industry during this period and in this area are the common concern of archaeology and metallurgy circle. To find out the application and technics of Gaogouli irons, pieces of ironware excavated from the fourth cultural deposit in Wunu mountain city were analysed by metallographic method and SEM-EDX. The results showed that the materials of iron objects included cast iron, gray cast iron partly, low carbon steel and wrought iron. The weapons and tools were made of steel annealed by cast iron with less impurity while nail was mad of puddling iron. Besides, semi finished iron showed the features of mixing by the pig iron mixing with wrought iron by collapsing and forging. It provided the metallographic deomonstration for applying the Guan Gang method melting and pouring pig iron into wrought iron for acieration. The metallographic study of Gaogouli iron artifacts reveals profile of the development level of handicraft industry during the Gaogouli metaphase.