In order to reveal the nature of the stress corrosion of Ti theoretically, the a tomic cluster model of α-Ti and the crack formed by dislocation accumulation wa s set up. The electronic structure parameters (Fermi energy level, structure ene rgy, surface energy, cluster energy and environment-sensitive embedding energy) of α-Ti and the crack were calculated by using the recursion method. The calcul ated results show that the environment-sensitive embedding energy of H atoms in the region of crack is smaller than that in the perfect area of α-Ti, so H atom s are apt to segregate at the crack. The positive cluster energy of H atoms in t he region of the crack in Ti metal shows that H atoms can not form cluster and h ave the tendency of forming ordered phases (hydrides). When H atoms accumulate o n the surface of the crack, they reduce the surface energy of the crack, making the crack propagation easier. The Fermi energy of the tip of crack is higher th an that in other areas, so electrons move to the perfect region of α-Ti from th e tip of crack, leading to the formation of the potential difference between the crack tip and the perfect region of α-Ti, then the dissolution-corrosion proce ss of crack tip as anode occurs under the action of the electrolyte.