The difference between flat feet and normal feet is mainly reflected in the appearance and morphology, function and secondary changes. 1. Appearance and morphology: Flat feet are flatter than normal feet due to the obvious collapse of the arch. Comparison with normal feet reveals that the dorsum of the foot is flatter and flatter, the forefoot is wider, and there is excessive bony elevation on the inside of the arch of the flat foot. 2. Function: Due to the low, flat and collapsed arches, flat feet have a reduced ability to cushion shock, elasticity and strength compared to normal feet. As a result, the foot’s ability to move is insufficient, and the corresponding pain symptoms appear after standing or walking for a long time. 3. Secondary changes: Due to the long-term weight-bearing imbalance of the foot caused by flat feet, it can lead to the weight-bearing imbalance of the ankle joint, which can easily cause secondary bone injury and strain of the foot and ankle, thus producing pain and dysfunction of the foot and ankle. Normal feet usually do not show secondary changes.