Old Industrial Area is such an area emerging during industrialization, which has exist in developed countries with highly industrialization for half an century. The traditional industries like mining, pulp and paper, and the iron steel industry dominated the areas for a long time in the past, and the industrial structure was unbalanced. When the dominant industry declined and the new one had not been established, the whole area appeared economic depressing step by step. Although China has a short industrialization, some regions are the same as ones in developed countries, especially in Northeast China. With enormous capital asserts, many state-owned enterprises and a large number of workers, the northeast of China played an important role in process of Chinese modernization in the past. However, with the rapid industrialization of China and affected by the global economy, some areas are declining because of the being exhausted resources and facing the industrial shunt and labour transfer, or because of low technology development compared with other cities. Some researchers have studied these areas, but they looked them as an unit ignoring the difference among areas or they sampled one area to study without suggestion to national macro-planning though it is useful to regional development. So, the paper supplies a gap and aims to classify the old industrial areas which are really solve the problem of unbalanced development of PRED in Northeast China. Based on the relevant research at home and abroad, the authors briefly introduce the forming background and relative mechanism of OIA, and from the dimension of time and space mainly defines OIA. Then, the authors establish the indicator system believing that the indicator system should include span index and current index, and the method flow of classification. With this system and method, the authors separate 10 OIAs from Northeast of China, which are Fushun, Fuxin, Jixi, Hegang, Shuangyashan, Daqing, Yichun, Qitaihe, and Liaoyuan. At last, as to the forming causes, the paper puts forward macro direction in OIA's development from the choices of dominant industries and the adjustment of the industrial structure.