Pain (Pain) is an unpleasant subjective sensory and emotional experience associated with tissue damage or potential injury. It consists of two components: pain sensation and pain response. Pain sensation: It is the human sensation of pain, which is unique to humans and occurs mainly in the cerebral cortex. Pain response: refers to a series of somatic and visceral reactions produced by injurious stimuli, often intertwined with autonomic activity, motor reflexes, mental and emotional reactions, from lower animals to all people have a pain response. Pain in animals is the pain response. The pain response may occur at all levels of the central nervous system and is mainly manifested by increased heart rate, increased blood pressure, altered respiratory movements, dilated pupils, sweating, fear, painful expressions, etc. Pain mechanisms: Studies have concluded that the cerebral cortex is the higher center where the sensation and response to pain are initiated. Nociceptive receptors are free nerve endings located in the skin and other tissues. Various injurious stimuli acting on the body can cause the release of histamine, bradykinin, 5-hydroxytryptamine and other pain-causing substances from damaged tissues. These substances act on the free nerve endings, causing nociceptive impulses to be rapidly transmitted along the afferent nerves to the spinal cord, up through the spinal thalamic tract and spinal reticular tract to the thalamus, and projected to the cerebral cortex to cause pain 1. The World Health Organization (WT0) classifies the degree of pain as follows: O degree: no pain; Ⅰ degree: mild pain, intermittent pain, without medication; II degree: moderate pain, continuous pain, affecting rest, requiring painkillers; III degree: severe pain, continuous pain, unable to relieve pain without medication; Ⅳ degree: severe pain, continuous severe pain with changes in blood pressure and pulse, etc. 2. Numerical Rating System (NRS): Numerical Rating System (NRS): The Numerical Rating Scale of Pain Level (see figure) is used to assess the pain level of patients. The degree of pain is expressed by 0-10 numbers in order, with 0 indicating no pain and 10 indicating the most severe pain. The patient chooses a number that best represents his or her pain level, or the healthcare provider asks the patient: How severe is your pain? The healthcare provider selects the corresponding number based on the patient’s description of the pain. The pain level is classified according to the number corresponding to the pain: mild pain (1-3), moderate pain (4-6), and severe pain (7-10). 3.Grading method according to the degree of pain complained of (VRS method) It is a combination of pain measurement scale and oral scoring method. It is divided into five grades: no pain, mild pain, moderate pain, severe pain, and severe pain. Mild pain means that the pain does not affect sleep at all; moderate pain means that the pain affects sleep, but can still fall asleep naturally; severe pain means that the pain causes inability to sleep or waking up in pain during sleep, and requires medication or other means to assist sleep; severe pain means that the pain is unbearable and worse than death. 4.Visual simulation method A long line (usually 100mm long) is drawn between no pain/ severe pain, and no markings, numbers or words are made on the line to avoid affecting the assessment result. One end represents no pain and the other end represents severe pain, so that the patient can draw a crossed line on the line that best reflects their pain level. 5. Pain intensity score Wong-Baker face It may be difficult to assess pain in infants or in patients who are unable to communicate using the aforementioned method. It can be assessed by drawing pictures with different facial expressions: no pain, a little pain, slightly painful, more painful, very painful, and most painful. 6, Therapeutic assessment of neuropathic pain Because the pain treatment effect of patients with neuropathic pain does not correlate well with pain intensity or certain drugs, the numberneeded to treat (NNT) score is often used to evaluate the analgesic efficacy of therapeutic drugs. In clinical practice, one way to describe the effectiveness of a drug is to calculate the number of patients needed to treat (NNT) plus a 95% confidence interval to achieve a defined degree (usually 50%) of pain relief in a patient. This method can be used as a clinically relevant comparison of different drugs or diseases. Equally important as the NNT in determining drug efficacy is the evaluation of drug-related harmful effects, i.e., counting the number needed to harm (NNH) for a patient to experience significant or intolerable side effects. For many drugs with unclear efficacy, the NNT/NNH ratio is a more appropriate approach, and drugs with low NNT/NNH ratios are superior to those with high NNT/NNH ratios. For the same class of drugs for different painful traits or different drugs for the same painful trait, NNT measures of drug efficacy do not reveal large or consistent differences, and establishing NNT/NNH ratios is of clinical guidance value for each drug and for various painful states.