In this paper, the stress distribution of Si/Ge interface and the mechanism of the point defect buffer layer in the stress release process of Si/Ge structure on a nanoscale are studied by the molecular dynamics method. The results show that in a one-dimensional interface model, the stress relaxation at the Si/Ge interface is closely related to the size of Ge of the simulation, and there is an approximately linear relationship between the decrease rate of interface stress and the size of Ge. The vacancy defect is introduced into the Ge film near the Si/Ge interface, and a point defect rich buffer layer forms, reducing the stress at the Si/Ge interface significantly. As the defect density in the buffer layer increases, the interface stress decreases step by step. Moreover, in the paper examined also is the mechanism by which the buffer layer affects the interface stress. The relationship between the stress variation caused by the point defect in the pure Ge structure and the defect density is compared and analyzed. The introduction of the defect buffer layer and the increase of the defect density can accelerate the release of the Si/Ge interface stress. The internal mechanism of the stress reduction would be that the defect introduces the compressive stress, which can offset the tensile stress generated by the lattice mismatch of the Si and Ge structure. Then the Si/Ge interface stress is reduced. Besides, as the defect density increases, the compressive stress introduced by the defect increases and the interface stress decreases. The examination shows that the introduction of the defect buffer layer into the growth of the pure Ge film on silicon can reduce the probability of the dislocation defect by structuring the buffer layer to reduce interface stress. And this method is indirectly confirmed by preliminary study of silicon-based Ge film growth with low-temperature buffer layer method.