Probabilistic safety assessment procedure is used to evaluate the cylindrical pressure vessel of 16MnR steel, which regards defect sizes, mechanical properties and stresses as random variables. Monte-Carlo simulation is applied on calculating failure probability, which is based on the Chinese safety assessment procedure (GB/T 19624-2004). Sensitivity analysis is performed to estimate the effect of change in input parameters. The results show that failure probability may be influenced significantly by change in parameters concerning yield strength and film stress. Additionally, the different distributions of input parameters have an effect on failure probability.