The oxide film, which is formed on the Zr-2.5% Nb pressure tube surface serves as a protective barrier against hydrogen ingress. Hydrogen ingress is a diffusion process and therefore is affected by the distributions of oxide orientation, grain size, shape, and boundary. Our previous research has focused on understanding the oxidation mechanism and predicting the hydrogen ingress and oxidation kinetics. In this paper, a simple model has been established to simulate the effects of cracks/voids on diffusion process. This model can be potentially used to study the influences of oxide cracks on hydrogen permeation. The effects of the volume fractions, orientation and distributions of cracks on the steady state diffusion flux are simulated.