Objective To observe the effects of dexmedetomidine on postoperative mechanical pain threshold, and to identify whether Dex can prevent postoperative hyperalgesia induced by remifentanil. Methods we taked the completely random grouping method. 60 patients undergoing elective Thyroidectomy were randomly divided into three groups: dexmedetomidine group (HD group ) The patients received dexmedetomidine 1.0 ug•kg-1 in10min before induction of anesthesia, and given 0.4 ug•kg-1•h-1 continuous infusion of Dex until 1 hour before the end of surgery, and given remifentanil 0.2 ug•kg-1•min-1. low dose remifentanil group (LO group ) and high dose remifentanil group(HI group),The patients received normal saline infusion replaced Dex, given remifentanil 0.05 ug•kg-1•min-1 and 0.2 ug•kg-1•min-1 respectively. Mechanical pain thresholds on forearm and periincisional area were assessed by von Frey filament. mechanical pain thresholds were recorded before surgery, and at 2, 4, 8, 12, 24, 48h postoperation, additional VAS score and postoperative adverse reactions within 48h were recorded. Results Mechanical pain threshold described by the median, interquartile range (M ± QR) ,compared Mechanical pain thresholds on forearm with the preoperative（13.2±42.6）, mechanical pain thresholds in the HI group（9.8±28.5）,（11.3±21.6）,（7.6±14.4）,（6.0±24.7）,(8.2±17.9), (8.0±19.5) are significantly decreased（P＜0.05), In the HD group at 8h（15.9±58.5）, 12h（22.3±62.8）, 24h（30.5±72.2）, 48h（19.9±109.3）, compared with the preoperative（10.2±19.2）,are significantly increased（P＜0.01）, and decreased in the LO group,but the difference was not statistically significant（P＞0.05）.The HD group （15.9±58.5）,（22.3±62.8）,（30.5±72.2）are higher at 8, 12, 24h compared with the HI group（7.6±14.4）,（6.0±24.7）, (8.2±17.9)（P＜0.05), HI group compared with the LO group（14.8±45.5）,（19.4±32.1）,（16.7±24.2）,（13.3±33.3）,（16.1±21.1）,（15.3±25.6） is significantly lower in the postoperation（P＜0.01）.The change in pain threshold on the periincisional area was similar among the groups. Additional VAS values compared with preoperative were significantly increased(P=0.004), but VAS value compared among the three groups is not statistically significant .Conclusion the application of dexmedetomidine in Thyroidectomy can increase postoperative mechanical pain threshold ,which can prevent remifentanil induced postoperative hyperalgesia.