OBJECTIVE： To observe the effects of dexmedetomidine combined with ulinastatin on stress reaction indexes， extravascular lung water value （EVLW） and pulmonary vascular permeability indexes （PVPI） and other parameters in one-lung ventilation （OLV） lobectomy patients. METHODS： A total of 80 patients underwent OLV lobectomy selected from the Affiliated Hospital of Southwest Medical University during Nov. 2015-Nov. 2016 were divided into control group （group N）， ulinastatin pretreatment group （group U）， dexmedetomidine continuous pump group （group D）， ulinastatin pretreatment+dexmedetomidine continuous pump group （group U+D）， with 20 cases in each group. Thirty min before anesthesia induction， all patients were given atropine sulfate 0.5 mg intramuscularly and received catheterization of right internal jugular vein and ipsilateral femoral artery under local anesthesia.  Based on that， group N was given 0.9％ Sodium chloride injection 100 mL intravenously； group U was given sodium chloride mixed solution 100 mL containing Ulinastatin for injection 200 000 U intravenously； group D was given continuous intravenous pump of Dexmedetomidine hydrochloride injection 2 μg/mL mixed with sodium chloride mixed solution at 1 μg/（kg·h）， and after induction intravenous pump at 0.5 μg/（kg·h） until the end of surgery； group U+D was given Sodium chloride mixed solution containing 200 000 U ulinastatin 50 mL and 4 μg/mL dexmedetomidine sodium chloride mixed solution 50 mL intravenously （same dose as above during induction period and maintenance period）. The levels of blood glucose， partial pressure of oxygen [p（O2）]， adrenocorticotropic hormone （ACTH）， norepinephrine （NE）， heart rate （HR）， cardiac output （CO）， systemic vascular resistance （SVR）， EVLW and PVPI were compared among 4 groups 30 min before anesthesia induction （T1）， 2 h after the beginning of surgery （T2）， immediately after extubation （T3） and 12 h after surgery （T4）. Liquid intake and output volume were recorded during T2-T4. The occurrence of ADR among 4 groups was observed. RESULTS： There was no statistical significance in each index among 4 groups at T1 （P＞0.05）. During T2-T4， the levels of blood glucose， ACTH， NE， SVR， EVLW and PVPI in group N were significantly higher than other 3 groups， and group U and D were significantly higher than group U+D， with statistical significance （P＜0.05）； there was no statistical significance between U and D （P＞0.05）. The levels of p（O2） and CO in groups U+D were significantly higher than other 3 groups， with statistical significance （P＜0.05）； there was no statistical significance among other 3 groups （P＞0.05）. HR of group N and U were significantly higher than other 2 groups， with statistical significance （P＜0.05）. There was no statistical significance between group N and U， between group D and U+D （P＞0.05）. There was no statistical significance in liquid intake or output volume among 4 groups （P＞0.05）. No obvious ADR was found in 4 groups. CONCLUSIONS： Dexmedetomidine combined with ulinastatin can significantly relieve stress reaction， and reduce the levels of part blood flow and respiratory dynamics indexes as EVLW， PVPI in patients with OLV lobectomy so as to play lung protective effect.