The olfactory nerve is the nerve fiber that runs from the olfactory epithelium through the sieve plate to the olfactory bulb. The ability to smell is a characteristic of the olfactory cells in the nasal mucosa. Injury to the nasal mucosa, olfactory bulb, olfactory filament or central nervous system connections may affect the sense of smell. Clinical manifestations are hyposmia, olfactory loss, olfactory deficit, olfactory inversion, phantom sniffing and increased sensitivity to olfactory stimuli. Patients with olfactory impairment usually do not affect their daily work and study. Patients with olfactory impairment should be further examined for the cause and treated for the right reason. Patients with olfactory hypersensitivity are rare, but according to the cases that have been reported, patients are very sensitive to olfactory stimuli, so that it becomes the source of discomfort. We need to detect and treat them early. Clinical examination is mainly as follows. 1.Cerebrospinal fluid examination. 2.Cranial base radiography, cranial CT and MRI examination. 3.Other necessary selective examination items such as blood routine, blood electrolytes, blood sugar, urea nitrogen, etc. 4.Other necessary selective auxiliary examination items include chest X-ray, electrocardiogram, etc. 5.Ear, nose and throat examination and olfactory examination.