This paper presents a 3D biomechanical model of a female body, which consists of elastic breast and rigid body on the basis of analyzing the biomechanical characteristics of human body. Bra is regarded as material linearity and geometric non-linearity. The contact between human body and bra is modeled as dynamic sliding interface based on the theory of contact mechanics. Finite element method is used in the time domain for deriving numerical solution of the dynamic contact problem. An example is presented to illustrate the simulation results of the computational model: a female human model is walking at a constant speed when wearing a bra. The computational model can simulate and characterize the dynamical mechanical behavior of the breast and bra during the body movement with the breast falling and bouncing in terms of bra deformation, pressure and stress distributions and breast stress distributions. Comparing with the quantity of measured garment pressure reported in the literature, the predicted pressure is close to the magnitude of experimental measurements, indicating that the model is able to simulate bra pressure during wear with reasonable accuracy.