The finite element modeling of a human foot and the simulation of the gait motion with a spontaneous plantar flexion were performed. The information on the human foot shape including the detailed interior structures were taken using the magnetic resonance imaging (MRI). Using the collection of the MRI images, a 3-D digital model of the human foot was reconstructed. The digital model was used for generating the finite element mesh of the human foot. Experimental measurement of the 3-D motion of the human foot, the reaction force and the contact area on the plantar with the floor was carried out. The experimental results were used as boundary conditions in the finite element simulation. The spontaneous plantar flexion during the gait motion was modeled as a displacement boundary condition at the heel, which mimics the role of the Achilles’ tendon. The finite element simulation results clearly illustrates that the spontaneous plantar flexion gives a substantial influence to the gait motion, and can be well modeled with the displacement boundary condition. Finally, the potential of the finite element simulation technique as a monitoring tool of the mechanical loading inside the foot was demonstrated.