Abstract： Objective To explore the prevention and treatment effect and its mechanism of Xuebijing injec-tion combined with dexamethasone on rats' paraqnat-induced acute and chronic pulmonary injury.Method One hundred and twenty of male Wistar rats were randomly divided into six groups:nomud group(A),administrated with saline;model group(B)and treatment groups(group C,D,E,F)were given 20%PQ(100 mg/kg.ip),and 2 hours later the normal and model groups were administrated with the same volume of saline for treatment,rats in group C and group D received 1.25 g/kg and 2.5 g/kg Xuebijing injection respectively.rdts in group E received 25,ng/kg dexamethasone,rats in group F receired 2.5 g/kg Xuebijing injection combined with 2.5 g/kg dexamethasone,one time per day till to be killed,while rats killed at 28 d were treated for 7 days.At 2 d,3 d,4 d after poisoned,five rats in each group were killed,serum SOD,MDA level and arterial gas(at 3 d)were measured.At 28 d,the rest of rats were killed,and serum TGF-β1,lung tissure HYP were measured.The pathology of the lung tissue was ob-served at 3 d and 28 d in guoup A,B,F.Results Compared with group B,poisoning symptoms in the treatment groups were milder and serum.SOD,MDA,TGV-β1,lung tissure HYP level were better,arterial oxygen content were higer.Among treatment groups,the treatment effects in group F were the best,SOD and MDA of 3 d,HYP and TGF-β1 of 28 d in group B and F were respectively(37.47±13.00,91.86±21.35)nmol/mL;(11.34±3.07,5.63±1.58)nmoL/mL;(2.54±0.63,1.32±0.07)mg/g;(484.13±63.79,202.22±49.83)pg/mL.The difference was significant(P＜0.05).The pathology of the lung tissue showed that acute lung hemorrhage,edema or chronic pulmonary fibrosis in group F were milder than that of group B.Conclusions In early stage,Xuebijing injection combined with dexamethasone has a stronger ability to clear out oxidized free radical and inhibit lipid super oxidized reaction.This may ameliorate acute pulmonary blooding and edema.In later stage,they could ameliorate chronic pulmonary fibrosis by inhibiting TGF-β1 secretion and HYP generation.