The mechanical state at the crack tip is one of the major factors affecting the stress corrosion cracking (SCC) growth rate in structural materials of the nuclear power plant. To understand the crack growth driving forces and their effects on SCC growth rate in the whole process of SCC, a finite element model of the growth process of SCC was built by using a commercial software ABAQUS, sequentially the working load, residual stress, and the film induced stress produced by the oxide film formationin front of the crack tip during SCC initial stage were discussed in this paper. The results indicate that the film induced stress produced by the formation of oxide film is the main crack growth driving force during the initial stage of SCC. While the working load and residual stress gradually become the main crack growth driving force as SCC crack advances.