The startle reflex disappears normally at 3 months of age and can disappear as late as 4 months. The startle reflex is one of the human infant reflexes and is most evident especially when the infant is lying on its back and is suddenly stimulated, which can be manifested by the infant’s arms being straightened, back being extended or bent, legs being straightened, and arms being clasped to each other. This reflex shows the infant’s ability to reach out and grasp the mother’s body when faced with a sudden situation. Under normal circumstances, this reflex disappears when the infant is 4 months old, but if it is still present beyond 4 months, the infant may have neuropathy; beyond 6 months, neuropathy is considered; if there is an asymmetric response in the upper extremities, hemiplegia, brachial plexus injury, clavicle or humerus fracture may be suspected; if the response in the lower extremities disappears, lower spinal cord injury and congenital hip dislocation are suspected. In conclusion, there is no need to worry too much about the presence of startle reflex in infants under 4 months of age, but if it still exists after 4 months, it is recommended to go to the pediatric department of the hospital to improve the relevant examination in order to exclude neuropathy or fracture or dislocation.