Abstract: Previous studies on shoe fit mainly focused on the compatibility between the shoe's last size and the wearer's foot size. Restricted by individual foot size change, footwear habit and design factor, it is difficult to achieve highly matching foot-type footwear products. Studies have confirmed that ill-fitting footwear was the main cause of foot pressure and skin friction and could also cause the change in walking posture. To further explore the influence of ill-fitting footwear on human gait and establish the relationship between shoe fit and plantar pressure distribution, a questionnaire survey was conducted, in which 9 subjects were asked about their subjective feelings of shoe fit. X-ray machines were further adopted to confirm the matching status of the subjects' feet and shoes, and Footscan plantar pressure plate was used to collect the peak value of plantar pressure and the trajectory of plantar pressure center of the subjects under the three conditions of shoes being too small, too large and moderate. Results showed that, when the shoe size changed, the peak value of plantar pressure and the locus of plantar pressure center changed. Compared with the shoes-fitting condition, the peak value of plantar pressure in the toe, the first metatarsophalangeal joint, the fifth metatarsophalangeal joint, the arch and the heel of the foot were significantly different (p<0.05) under the conditions of shoes being too small and too large. Shoe size changes significantly affect the distribution of plantar pressure.