The Study of the ERP system implemented by the major steel mills in mainland China - a case study on Wuhan Iron & Steel Co. Since 1990s, the radical change of customer demand, short life cycle of products, and accelerating innovation of technology have driven the enterprises to carry on reform of the management style and renewal of the management skill. The reform of the management style is focused on BPR (Business Process Re-engineering), and the renewal of management is to implement ERP (Enterprise Resources Planning) system. It is generally recognized that information technology can upgrade the enterprise competence. Applying information technology on BPR to facilitate ERP implementation is also proved to be successful. Both of them are important elements to improve business management. This research employs empirical studies about the implementation of ERP in large steel mills. Being different from the traditional manufacturing industries, the production type of large steel mills is a pyramid-shape model with higher difficulty, more financial and resource inputs. There are four different implementation modules based on the cases studied in this research: 1. Start from the rationalization of business administration, and self-develop a proper ERP system; 2. Look for assistance from the experienced intra-industry companies, and collaborative-develop a system required; 3. Look for assistance from the consultant companies to integrate the package software; and 4. Look for assistance from the software companies with domain knowledge in the early period, and start self-developing in the late period. All the implementing methodology, organization structure and principles of the four modules are described in this article. It is also our hope that the research result can help the enterprises to build up ERP.