Fracture process of creep fatigue in a Type 304 stainless steel at 923K can be divided into two types; “crack initiation type” and “crack growth type”. The former is characterized by multiple small cracks initiating one after another along grain boundaries on the specimen surface and coalescing each other at the late stage of failure life, when the material is subjected to relatively large strain ranges in slow tension-fast compression (so called c-p type) strain waveforms. This failure is mostly governed by crack initiation. The latter is distinctive of the initiation and growth of little coalescence, which is revealed under small strain ranges and/or in slow-slow (c-c type) or slow very slow (c-s type) strain waveforms. Therefore, the failure life is controlled by the growth rate of small cracks in this case. In this study, a numerical simulation was done based on a model of two kinds of driving forces for crack initiation and crack growth with random fracture resistance of grain boundaries, in order to distinguish between the two types of fracture process and to estimate the failure life in relation to the cracking behavior.