ObjectiveTo compare the effect of three kinds of intrinsic foot muscle exercise on flatfoot. MethodsFrom September to November, 2022, 45 subjects with flatfoot from Capital University of Physical Education and Sports were randomly divided into short foot exercise (SFE) group (n = 15), toe-spread-out exercise (TSOE) group (n = 15) and short foot & toe-spread-out exercise (SF+TSOE) group (n = 15), who received SFE, TSOE and SF+TSOE, respectively, for eight weeks. The cross-sectional area of abductor hallucis muscle, navicular drop test (NDT) and Chippaux-Smirak index (CSI) were measured before treatment, four weeks after treatment and eight weeks after treatment. ResultsThree subjects dropped out in each group. The main effect of time was significant for left and right cross-sectional area of abductor hallucis muscle, NDT and CSI (F > 13.906, P < 0.001). The main effect of group was not significant for left and right cross-sectional area of abductor hallucis muscle, NDT and CSI (F < 1.934, P > 0.05). The interaction effect of group and time was significant for left and right NDT (F > 3.044，P < 0.05), and it was better in SF+TSOE group than in SFE group and TSOE group (P < 0.05). ConclusionSF and TSOE can improve the cross-sectional area of abductor hallucis muscle and foot morphology in subjects with flatfoot, and the combination of them may be more effective.