Objective: To study the effect of dexmedetomidine combined with ulinastatin on RAAS system, coagulation indexes and oxygen free radicals after acute aortic dissection surgery. Methods: A total of 48 patients with aortic dissection who accepted endovascular graft exclusion treatment in the hospital between May 2014 and February 2017 were selected and randomly divided into two groups, group A received dexmedetomidine, ulinastatin combined with general anesthesia, and group B received general anesthesia. The RAAS hormones, coagulation indexes and oxygen free radical indexes were measured 1 day before surgery, during operation and 24 hours after surgery. Results:During operation and after operation, serum REN, AT-II, ALD, FIB, DD, MDA and MPO contents as well as APTT and TT levels of both groups of patients were significantly higher than those before operation while TAOC and TSOD contents were significantly lower than those before operation, and serum REN, AT-II, ALD, FIB, DD, MDA and MPO contents as well as APTT and TT levels of group A were significantly lower than those of group B while TAOC and TSOD contents were significantly higher than those of group B. Conclusion: Dexmedetomidine combined with ulinastatin for acute aortic dissection can inhibit RAAS system and oxygen free radical generation and improve coagulation function.