The T4 impeller for cracked gas compressor, a megaton device, is studied. The parametric finite element model is established using finite element software. On the basis of the artificial neural network (ANN) technique, the stochastic perturbation method, the differential matrix and the reliability theory, some point physical dimension are defined as basic random parameters. The reliability analysis model is established with the criterion that the maximum stress of the T4 impeller is no more than yield strength of material. The influence degree of the parameters on the reliability of the T4 impeller is obtained by the sensitivity analysis and the non dimensional analysis, which provide more theoretic evidence for the impeller design in engineering practice.