Many of the specific safety evaluation methods, such as Failure Mode and Effects Analysis, Preliminary Hazard Analysis, Safety Checklist, are used in the schematic design phase. Being applied as concrete techniques in a micro level, it is difficult for them to provide sufficient confidence about safety in the actual use of products. This paper presents a new quantitative safety evaluation method based on argumentation technique. First, we discuss the basic principles and the theoretical basis of our method. Then, the basic steps of evaluation are given. Finally, through a case study, we verify the feasibility and effectiveness of the method. The results show that our quantitative method can be used as a comprehensively analysis method which includes many factors from the high level, such as design, management, human factors, environments. Compared with traditional approaches, our contribution presents a new way to assist decision makers, such as product designers and project managers, to make their decisions more objectively, reasonably, effectively.