Some structures such as components of deep-sea submersibles, will endure cyclic loads with a period of dwell time at high stress level within each loading-unloading cycle. For components subjected to cyclic loads, fatigue life analysis is an important issue. Approaches based on fracture mechanics are reliable, in which choice of crack growth model plays an important role. The commonly-used crack growth rate model can make fatigue crack increment by cycle-by-cycle integration, which neglects the crack length change within a single cycle. Some researchers proposed the concept of crack growth rate model in small time domain to consider the crack growth within one load-unload cycle. However, during the dwell time, the crack increment can also be detected. In this paper, the model in small time domain will be extended to that for a single load-dwell-unload cycle. The model can be applied to calculate the life of metal structures under dwell-fatigue conditions.