Visceral pain is primarily caused by disorders of internal organs, including dilatation, ischemia, inflammation, and pulling of the mesentery. Patients often exhibit combined symptoms such as nausea, fever, malaise and pain. There are five main clinical features of visceral pain as follows: 1. Not all visceral organs can produce pain due to uneven distribution of receptors or lack of appropriate injurious stimuli. 2. Visceral pain is not always injury-related, i.e., visceral pain has non-structure-dependent and non-function-dependent properties. 3, Because there is central convergence of visceral and somatic afferent nerves, visceral pain often involves the body wall. 4. It may be related to the distribution of afferent nerves, and visceral pain is rarely confined to a particular site and is diffuse. Fifth, visceral pain is often accompanied by obvious motor and autonomic reflex activity, which is likely a stress response of the organism to the outside world. Visceral pain needs to be differentiated as follows: 1. Genuine visceral pain: It is pain produced when the viscera itself is stimulated. It is a kind of dull pain, soreness or burning pain, and can also be colic. It is caused by the expansion, spasm or strong contraction of the cavity organs, the stimulation of chemical substances, and the pulling of the organs. Its characteristics are: (1) visceral pain is located inside the body and occurs more slowly but lasts longer; (2) lack of double pain; (3) unclear localization, and the edge of the pain area is not easily determined. 2. Body cavity wall pain: also known as similar visceral pain, it is pain caused by irritation of the wall layer of the body cavity, such as pain caused by inflammation, pressure, friction or surgery of the pleura and peritoneum. This kind of pain is also characterized by pain or nociceptive hypersensitivity in the skin of its corresponding spinal nerve segment.