TEM (Transmission Electron Microscope) observations show that corrosion process during stress corrosion cracking (SCC)enhances dislocation emission and motion; and microcrack of SCC initiates when the corrosion-enhanced dislocation emission and motion reaches a certain condition. The passive film or dealloyed layer formed during corrosion or SCC can induce a large tensile stress,which can assist the applied stress to enhance dislocation emission and motion, and then SCC occurs. Experiments show that the variation of SCC susceptibility of brass, α-Ti and stainless steel with the applied potential and pH value of the solution is consistent with that of the corrosion-induced additive stress. Molecular dynamics simulations show that a dealloyed layer can generate a tensile stress; and the corrosion (dealloyed layer)-induced tensile stress can assist the applied stress to enhance dislocation emission and crack propagation.