A numerical model of a cylinder of marine steam turbine was established for analyzing its reliability under the impact of fractured blades. In this model, the initial speed, mass, yield strength, modulus of elasticity of the fractured blades, as well as the elastic modulus, yield strength and ultimate strength of the cylinder material were taken as random variables. A certain number of samples were acquired using Monte Carlo method. The distribution of random variables was obtained via curve-fitting using a few samples among them. Then, 50 groups of initial values of random variables were obtained using the program for generating random variables, and the process of penetration of the cylinder was simulated with this model. The maximum equivalent stress of the cylinder was obtained. Adopting the ultimate strength criteria and W-testing, the maximum equivalent stress of the cylinder was validated to obey the normal distribution, and the destructive probability of the cylinder was obtained. A reliability analyi