Abstract: Probabilistic safety analysis (PSA) technology is attractive for the power plant owner and nuclear safety authority. While the application of PSA is used more widely and deeply, the demand for accelerating the calculation of software is more strict. However, the nuclear power plant is complex and its PSA model is very huge. As the work is more accurate, the model is expanding, which makes the calculation more difficult. NFRisk, an independent development software used for PSA, adapted two pre-treatment strategies, structure simplify and modularization, to handle this problem. It is proved that the strategies can accelerate the fault tree resolving and cut down the calculating time.