[Abstract] Background:Pain is an unpleasant sensory and emotional experience, along with existing or potential tissue damage. Objective:Enough attention to pain or pain assessment tool will relieve the pain of patients and bring good news for the patients. Content:Due to large individuality of the pain，lots of factors affect the perception of pain, so it difficult to calculate and compare objectively and accurately. As pain caused the physical and psychological injury to the patients, so we should look forward more effective method of pain assessment and effective pain management tools. For a variety of pain assessment tools, the specific operation for people are not the same. This review presented an overview on the objective pain assessment methods.Trend:The objective evaluation in pain is more important in clinic and it is useful in quantization of pain and for clinical practice