[en] The seismic margin assessment (SMA) is one of the nuclear power plant seismic safety evaluation methods. The calculation of high confidence for low probability of failure (HCLPF) value for the structure, system and components (SSC) is one of the important contents of SMA. The definition for HCLPF value and the conservative deterministic failure margin (CDFM) method which was used to calculate HCLPF value were introduced in this paper. The emergency diesel generator set and the main control building of Qinshan Nuclear Power Plant were taken as examples. Their HCLPF values were analyzed with CDFM method. Most of the HCLPF values of SSCs were obtained by this method to provide the foundation on which the SMA of Qinshan Nuclear Power Plant can be developed. (authors)