Hallux valgus is a common foot deformity characterized by hypermobility of the first metatarsal ray. The lower longitudinal arch is an intrinsic factor related to the lateral drift of the hallux. This paper conducted a quantitative study on the improvement of the first metatarsal and arch condition by arch support and used finite element analysis to simulate the bone displacement with the intervention of arch support. In this research, a foot arch support made of carbon fiber was developed and seventy-six female subjects were recruited for a two-month wear trial. Footprints of their dominant foot were measured to investigate the effect of the arch support on lifting the arch and correcting the hallux valgus pathology. Different foot parameters including foot length, foot breadth, heel breadth, arch angle, arch breadth, plantar arch index, foot type index, and hallux valgus angle were also compared. By using finite element analysis, the biomechanical effects of the arch support on the foot structure can be visualized. According to the results of the wear trial, the use of the arch support can significantly improve the arch curvature of the foot, while no significant correction of the hallux valgus angle was found. Among the arch parameters, the arch breadth and the foot type index are the key indicators to precisely characterize foot types and arch conditions. When a clear outline of the footprint is not available, arch breadth provides reliable association with the foot type index (R2 = 0.928). An arch breadth ≥ 4 cm is categorized as flatfoot. This article confirms the effectiveness of our arch support in lifting the arch over a two-month period and provides a scientific surrogate index to aid in diagnosis, which is important for therapeutic and diagnostic applications.