Intraoperative analgesia monitoring is a hot research topic in recent years. Well managed intraoperative analgesia monitoring can reduce the use of opioid analgesics, reduce the incidence of dysphoria during the recovery period, reduce the incidence of moderate and severe chronic pain after surgery, and shorten the postoperative recovery time of surgical patients. In recent years, some non‑invasive anesthesia analgesia monitoring equipment provide the index of parameters of the balance between analgesic effect and nociception, including surgical pleth index (SPI), analgesia and damage sexual stimulation index, the index of consciousness, and the pupil diameter measurement, etc. Among them, the SPI, is the target in many studies in recent years. This article reviews the clinical application of the SPI in general anesthesia. The basic principles, clinical applications, influencing factors, and limitations of SPI are described in this article, which will provide a basis for the application of SPI in clinical research in the future.