This study aimed to construct three-dimensional finite element model of the mandibular complete overdenture and to analyze the influence rules for stress distribution under different mandibular shapes. The layer cutting method was employed as a basic tool to deal with different plaster models to gain two-dimensional point data. These data were introduced to the commercial software ANSYS to construct three-dimensional finite element model of the mandibular complete overdenture, including nine kinds of typical shapes, such as sharpness, roundness and squareness, and etc. Static loads were imposed on denture so as to accomplish biomechanical analysis and to study the influence rules of stress distribution for mandibular complete overdenture under different mandibular shapes. Results revealed that the sequence of stress from high to low was squareness, roundness, sharpness and the other extrapolated, basic and inside. The three-dimensional finite element model has high simulation accuracy and the results provide an experimental foundation and guidance for clinical work.