Abstract: In the level one Probabilistic Safety Analysis (PSA) of High Flux Engineering Test Reactor (HFETR), the primary task is the initiating event analysis. In the present paper, the methods such as engineering evaluation, reference to the previous list of initiating events, deductive analysis and operational experience summary are applied comprehensively to determine the list of PSA initiating events in the HFETR operation period. Then, the initiating events are properly grouped. Combined with the methods such as fault tree analysis, HFETR operation event statistics and reference to the same type of research reactor, the frequency of each initiating event group is given, which lays a foundation for the subsequent level 1 PSA of HFETR.