Current SFTA methods highly rely on the experience of analysts and it's difficult to reuse history information of SFTA for current methods. With the increase of software complexity, the scale of software fault tree has increased explosively. Thus, there is an urgent need to effectively reuse history information of SFTA in order to avoid repeating analysis and improve efficiency. To organize fault tree information effectively, mine valuable patterns from history information and reuse SFTA information, this paper proposed a reuse-oriented auxiliary construction method for software fault tree. Firstly, a semiformal method is proposed to define software fault tree information, which includes elements such as node, relation, type, target function and target software module. Then a knowledge base for software fault tree information is constructed. History information is indexed and reconstructed from several different attribute dimensions. Finally, by text matching and intelligent linking, a reusable sub fault tree is generated automatically from the knowledge base and can be inserted into another fault tree, achieving the goal of reusing SFTA information. The method proposed in this paper can effectively provide aid for SFTA, improve analysis efficiency and increase automation degree. Meanwhile, a tool based on this method is introduced in the paper, which also includes some other useful features such as automatic alignment of nodes, rule checking, minimal cut set calculation, qualitative analysis, and report generation. An example is provided in the paper to demonstrate how to use this method and validate the applicability, validity and efficiency of this method.