Abstract: The MAAP5 code was applied for modeling of primary and secondary circuits, safety system and containment for Qinshan Nuclear Power Plant in this paper. And by applying the code, a severe accident scenario of large break loss of coolant accident (LBLOCA) at cold leg with failure of high-high, high, and low pressure injections and containment spray was selected for simulation and calculation, and some important transient process parameter change laws with time were given. The analysis results show that under the condition of no active intervention within 72 h, the integrity of the containment can be guaranteed and the relevant data of which can provide important reference for the establishment of accident prevention and mitigation measures of Qinshan Nuclear Power Plant.