Human perception includes two mental processes: sensation and perception. Sensation is the brain’s reflection of the individual properties of a thing, such as the shape, color, size, weight and smell of an apple, produced by objective stimuli acting on the sensory organs. Perception is the integration of different attributes of things on the basis of sensation, and the formation of an overall impression by combining previous experiences. For example, the impression of an apple in the brain based on its shape, smell, color, etc., combined with previous perceptions of apples, is a perception. Hallucination is a kind of illusory perception that occurs when no real stimuli are applied to the sensory organs. Hallucinations are one of the most common and important psychiatric symptoms. Hallucinations can be classified differently according to the sensory organs involved, their origin and the conditions under which they occur. According to the sensory organs involved, hallucinations can be classified as: hallucinations of hearing, vision, taste, smell, touch, and visceral hallucinations. Clinical hallucinations are common: 1. Auditory hallucination is a kind of unreal hearing, i.e., the patient hears a sound that does not exist. Hallucinations are the most common hallucinations in psychiatric clinics. Patients hear sounds that can be monotonous or complex; they can be verbal, such as comments, praise, insults, reprimands, or orders, or nonverbal, such as the roar of machines, the sound of running water, bird calls, etc. Among them, verbal hallucinations are the most common, and the hallucinated voice can be directly talking to the patient or the patient as a third party to hear the conversation of others. The content of the hallucinations is usually related to the patient and is often unfavorable to the patient, such as commenting on the patient’s words and actions, discussing the patient’s character, ordering the patient to do something dangerous, etc. Therefore, the patient is often distressed. As a result, patients are often distressed and disturbed by them, and may talk to themselves, curse to the air, refuse to drink or eat, commit suicide, injure themselves or destroy things. 2.Visual hallucination means that the patient sees something that does not exist. The content of the hallucination can be monotonous light, color or fragmented images, or complex characters, scenes, scenes and so on. Hallucinations that occur in a clear state of consciousness are most often seen in schizophrenia. If any of these manifestations are found, it is important to find a specialist to give confirmation for early detection and diagnosis to facilitate early recovery from the disease.