This paper investigates the stress distribution at the Si/Ge interface and the stress release mechanism of the point defect buffer layer with the molecular dynamics simulation method. The results show that the stress relaxation at the Si/Ge interface is closely related to the size of the X-Y plane of the simulation. The vacancy defect is introduced to the Ge film near the Si/Ge interface and a point defect rich buffer layer forms which reduces the stress at the Si/Ge interface significantly. In addition, the point defect buffer layer brings a new interface between the buffer layer and the Ge film called the defect interface, which has great impacts on the stress within the Ge films. Moreover, the thickness of the buffer layer influences stress both at the Si/Ge interface and the defect interface. The paper also examines the mechanism by which the buffer layer affects the interface stress. 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 defect density and thickness of the buffer layer to reduce interface stress.