Background:Preemptive analgesia is the initiation of analgesic regimen before the onset of nociceptive stimulation, preventing the amplification of pain due to peripheral and central sensitization and thereby reducing subsequent pain. Preemptive analgesia of DEX in the epidural and subarachnoid space can effectively prevent the central sensitization, and significantly reduce the phantom limb pain, residual pain after one year of lower limb amputation. Objective: To investigate the short and long-term effects of dexmedetomidine (DEX) in preemptive analgesia. Method:The patients undergoing noncardiac surgery were selected and divided into DEX group and Placebo group randmized. The DEX group was continuously pumped at 1.5 μg /(kg·h) for 15 minutes before induction, and after induction continue infusion 15min. the Placebo group was infused with equal amounts of isochronous normal saline.The Coprimary efficacy outcome was a composite of analgesia effect were the IOC2 target rate. Pain numeric rating scale was assessed with the (Numeric Rating Scale)NRS>3 as the composite pain outcome whenever at immediately, 2, 6, 12, 24, and 48 h after surgery.