Injuries of the base of the fifth metatarsal are among the most common of all skeletal injuries of the foot. The fracture is considered by previous research to be an avulsion due to the slip fascia, however, the mechanism of the plantar slip fascia’s function still not very clear. In this study, a detailed three-dimensional (3D) finite element (FE) model was developed by reconstruction of CT images. A sensitivity study was conducted to evaluate the effect of varying stiffness of the slip fascia on the fifth metatarsal’s deformation. The results showed that the largest vertical displacement was appeared in the metatarsal’s head part, and the difference was up to 10.5%, while the Young’s modulus of the slip fascia increasing from 50MPa to 500MPa.