Analytical discussion was given on the relationships between actual cavity distribution and creep damage parameters such as volume fraction of cavities, effective cross-sectional area and the 'A' parameter. The relationships between cavity distribution and these damage parameters were derived using a very simple probabilistic model where creep cavities on a grain boundary facet were initiated and grew, depending only on the macroscopic stress (or strain rate) acting on the facet. The exact relationships were represented by Eqs. (16), (20) [or (23)] and (26), respectively. These expressions take into account the effect of the size and direction of grain boundary facets. Damage evolution during creep and creep-fatigue can be calculated using these equations.