Abstract: This article gives a brief description of the features of TRAC-PF1 in connec-tion with the analysis of a large break LOCA. The model used for the analysisof large break LOCA by TRAC-PF1 for the nuclear steam supply system ofQinshan Nuclear Power Plant is described, the results of steady-state initializationcalculation, basic assumptions, sequence of events, and some curves of transientprocesses are presented. The results obtained are discussed, and the key input datafor obtaining the results of the analysis of large break LOCA of Qinshan NuclearPower Plant are pointed out. A method for analyzing large break LOCA usingTRAC-PF1 is recommended.