【Abstract】 Objective To investigate the efficacy of dexmedetomidine for multimodal analgesia on postoperative analgesia after arthroscopic knee surgery. Methods Ninety patients undergoing arthroscopic knee surgery were randomly assigned into three groups. Group A received i.v. saline 20 ml and intra-articular dexmedetomidine 1μg/kg and 0.25% ropivacaine 20 ml. Group B received i.v. 1μg/kg dexmedetomidine and intra-articular 0.25% ropivacaine 20 ml. Group C received i.v. saline 20 ml and intra-articular 0.25% ropivacaine 20 ml. Pain visual analogue scale (VAS) and sedation score of post-operation (1h, 2h, 4h, 8h, 12h, 20h, 24h) , duration of analgesia, the total postoperative analgesic use during the first 24 h and adverse reactions were evaluated. Result Compared with Group C, VAS score was reduced significantly for 1h, 2h, 4h, 8h in Group A and 1h, 2h in Group B after operation (P<0.05) , but intensity of pain was comparable in all groups after 12h. Compared with Group B, Ramsay score was lower significantly for 1h, 2h in Group A and Group C，and in 2h, 4h Ramsay score Group A was higher than Group C (P<0.05) , but Ramsay score was comparable in all groups after 8h. Compared with Group C, the duration of analgesia more longer in Group A and Group B ( P<0.01) and total consumption of fentanyl was significantly less in Group A and Group B ( P<0.01). The rate of bradycardia in Group B was higher than Group A and Group C (P<0.01). Conclusion Intra-articular injection of dexmedetomidine and ropivacaine can significantly relieve pain after arthroscopic surgery; reduce the use of opioids and prolong the duration of analgesia. Dexmedetomidine and ropivacaine applied to multimodal analgesia scheme for arthroscopic knee surgery can effectively control postoperative pain, and make patients painless in joint function rehabilitation.