During stress corrosion cracking of Cu3Au alloy, a dealloyed layer on the surface will be formed because of preferential dissolution of Cu. Molecular dynamics (MD) simulations showed that Cu3Au crystal with a dealloyed layer on one surface and one end fixed will be deflected after prolonged relaxation because of a tensile stress generated at or near the dealloyed layer interface. The deflection and then the tensile stress increases with the depth of dealloyed layer and the vacancy concentration in the dealloyed layer. MD simulations for a single edge crack under mode I loading show that, no matter what the crack orientation is, edge dislocation is first emitted from the crack tip followed by large amounts of screw dislocations as loading proceeds, and the crack begins to extend when dislocation emission and motion reach a certain condition. The critical stress intensity for dislocation emission is decreased from KIe = 0:62 MPam1/2 with no dealloyed layer around the crack (to simulate loading in air) to K*Ie = 0:58 MPam1/2 with a dealloyed layer introduced around the crack (to simulate SCC), and the critical stress intensity for crack extending after emitting large amounts of screw dislocations is decreased from KIp = 1:14 to K*Ip = 1:0 MPam1/2 correspondingly. This indicated that a dealloyed layer-induced tensile stress can help the applied stress to enhance dislocation emission and crack extension, and results in SCC.