Alzheimer’s disease is not a mental illness. The performance of dementia patients is mainly a decline in learning ability and significant memory loss. In the early stage, the patient’s recent memory is significantly reduced, and recent events can be easily overlooked. The patient manifests this by asking the same question over and over again, putting salt in a meal several times because he can no longer remember ever putting it in, or forgetting to turn off the heat when boiling water. In later stages, distant memory is also affected. The second manifestation of dementia patients is disorientation; they do not know where their home is, they often get lost, they do not know what year, month and day it is, and people they once knew very well are now unrecognizable, and they do not even recognize their own family members. People with dementia also have dyscalculia, being unable to buy goods and not knowing how much they should pay or how much they should find. Alzheimer’s patients also show emotional instability, which is easily accompanied by depression and sadness, so they need to be differentiated from patients with psychosis. Patients with psychosis are only mentally abnormal and are not accompanied by the other symptoms mentioned above.