The cost management and control are the important topic that most of enterprise operators have to confront with. Facing the increasing competition in enterprise environment, it is, in active respect, necessary to control the cost effectively in order to gain niche in keen market competition; in positive respect, it is to avoid any error policy decision because of inaccurate cost data. In traditional cost accounting, the allocation method of overhead is incomplete so that it is easier to result a distortion phenomenon in production cost structure. For the past years, the management academic world has proved through detailed study and real application that using the Activity-Based Costing (ABC) System can improve the defect of traditional cost accounting. The reasonable operation analysis and the exact cost driver allocation of ABC System will enhance the accuracy of the cost data. This case study company is a sole integrated steel producer in Taiwan. Due to the diversity of products, the company¡¦s production processes are extremely complicated and varied. The existing cost management system is unable to provide an actual cost under the different processes. Therefore, there is a room for improvement in analyzing the cost sharing of product expenses. This report takes the case study company¡¦s BOF plant as an example to research, by means of the process analysis, how to allocate the cost exactly, and to make a new cost system which can match the spirit of ABC. Meanwhile, this report makes a comparative analysis between the original cost system and ABC one. The result of the research revealed that the ABC cost system may truly improve the phenomenon of distortion of the product cost structure in the case study company. Using ABC cost system may not only promote the accuracy of the cost information, but also enhance the working performance under the activities analysis and control and reduce the waste of resources.