Background　Pain in awake patients can be assessed on the basis of their subjective description. But the pain assessment during surgery often depends on several vital signs and practitioners' clinical experience, and often lacks specificity and sensitivity.　Objective　To analyze and summarize recent studies in operative pain monitoring with surgical pleth index (SPI).　Content　This article presents the procedures and effectiveness of SPI in monitoring pain, and summarizes the application of SPI in perioperative pain monitoring. SPI can be used to assess the balance between nociception and anti-nociception to guide the use of analgesic drugs, to predict postoperative pain levels, and to analyze influencing factors of pain symptoms, as well.　Trend　SPI monitoring provides a new avenue for the assessment of perioperative pain levels.