Based on the Pairs-Erdogan crack growth model and with the application of the moment and a crack limit equation of state, the reliability of the steam floating machine under the circumstance of random variable basic parameters was discussed, and a steam-floating impeller crack growth reliability model was established. The reliability of impeller crack propagation life was deduced, which is basically the same with the results of Monte-Carlo simulation. The result shows that the method can give a more accurate forecast results and is suitable for application.