1. Routine assessment: For cancer patients with pain symptoms, pain assessment should be included in the routine monitoring and documentation of care and should be completed within 8 hours. Routine pain assessment should identify the cause of explosive pain episodes, such as pain due to pathological fractures, intestinal obstruction and other emergencies that require special management. 2. Quantitative assessment: It includes the most severe and least severe pain in the last 24 h, as well as the usual pain level. The common methods are numerical grading method (NRS), facial expression assessment scale method and grading method of pain level of complaints (VRS). 3. Comprehensive assessment: This principle refers to a comprehensive assessment of the cause and type of pain, pain onset (nature of pain, aggravating or relieving factors), pain relief treatment, vital organ function, psycho-psychiatric condition, family and social support, and past history (such as psychiatric history, substance abuse history). In the course of treatment, another comprehensive assessment should be conducted within 3 days of giving pain relief treatment or when stable remission is achieved, in principle no less than 2 times/month, often using the Brief Pain Assessment Inventory (BPI). 4.Dynamic assessment: It includes changes in the degree and nature of pain, episodes of explosive pain, factors of pain reduction and aggravation, and adverse reactions to analgesic treatment, etc. Dynamic assessment is particularly important for dose titration of drug analgesic therapy.