Abstract: In the cut sequence set(CSS) model, in order to get the minimal cut sequence set(MCSS) from the primary form of CSS,which is transformed from dynamic fault trees(DI}I})，the inference rules of sequence failure symbol(SFS)were put forward. The rules, which include combination law, or distribution law, and distribution law, absorption law,CSP law and WAP law,were established according to the sequence of basic events and the SFS. The proofs of the rules were provided. The paper also listed some inexistent cut sequences in reality, and provided some educed rules that can be got from the inference rules. SFS inference rules are the formalized qualitative analysis of CSS model. And they can be used to automatically get the MCSS of dynamic systems and design the computer assisted tools.

Key words: Cut sequence set,Sequence failure symbol,Inferencc rules,Dynamic fault tree,Reliability