[en] The key steps about nuclear power plant PSA-based seismic margin assessment are discussed in this paper. The analysis points include selection of seismic margin earth level, civil structures screening criteria, attentions about plant walkdown, HCLPF definition and the basic principles about CDFM compute the seismic margin capacity of structures. The methods and principles about HCLPF calculation are demonstrated by the nuclear power plant shear concrete walls. The study conclusion and experience can provide reference for the nuclear power plant seismic margin assessment and determine the nuclear power plant seismic margin capacity. (authors)