Objective To explore the relationship between plantar fascia stiffness and windlass mechanism and their impact on the arch, and provide a biomechanical mechanism explanation for plantar fascia and arch-related problems. Methods A foot-plate model with 30° flexion angle at the metatarsophalangeal joint was constructed. The musculoskeletal model combined with the three-dimensional finite element analysis method was used, and the dynamic data of the foot during walking at the speed of 5 km/h was obtained using dual fluoroscopic imaging system (DFIS). The finite element model was verified, and the influence of plantar fascia stiffness on the capstan mechanism and arch-related mechanical parameters was explored. Results The finite element simulation analysis results were highly consistent with the foot data obtained by DFIS, confirming the validity of the model. With the increase of plantar fascia stiffness, the windlass effect and the stiffness of the longitudinal arch of the foot both showed an increasing trend, but the flexion angle of the metatarsophalangeal joint decreased, the distal stress of the plantar fascia gradually decreased, and the proximal stress increased; when the plantar fascia stiffness was 25%–150%, the width of the transverse arch of the foot increased with the increase of plantar fascia stiffness, while the height of the transverse arch decreased with the increase of plantar fascia stiffness; when the plantar fascia stiffness was 150%–200%, the width of the transverse arch of the foot decreased, the height increased, and the stiffness also increased. Conclusions An increase in plantar fascia stiffness can enhance the windlass mechanism to some extent, but it also leads to a reduction in metatarsophalangeal joint flexion. The stiffness of the plantar fascia affects the metatarsophalangeal joint flexion, thereby impacting the windlass mechanism and the distal tensile force of the plantar fascia. Together with the ground reaction force at the distal end of the metatarsals, these factors collectively influence the stiffness of the transverse arch of the foot.