Abstract： Objective To investigate the clinical efficacy of the treatment with long-term NIPPV in patients with stable severe COPD complicated with respiratory failure,and the impacting on serum levels of MMP-9.Methods We selected prospectively 80 outpatients of stable severe COPD complicated with respiratory failure which were divided into two groups (experimental and control group,each group 40)according to their ability to tolerate and accept the long-term NIPPV treatment,two groups of patients were given oxygen therapy,slow-release oral theophylline,and inhalation of tiotropium for one year,and added to 1 year NIPPV therapy in experimental group.The outcomes measured included the followings:SGRQ score,MMRC score,6-MWD,PaO2,PaCO2,FEV1 ％pred,the serum levels of MMP-9 and the rate of acute exacerbations of COPD and hospital days in last 1 year and following 12 months.Results After 1year,the differences of SGRQ score,MMRC score,6-MWD,PaO2,PaCO2,FEV1％ pred,MMP-9 in the experimental group [(63.60 ± 3.92) scores vs (51.93 ± 3.77) scores,(3.65 ± 0.48) scores vs (2.43±0.50) scores,(158.85±6.39) mvs (248.00±9.32) m,(56.98±1.63) mm Hg vs (66.58±2.23) mm Hg,(60.58±2.89) mm Hg vs (51.55±2.28) mm Hg,(38.68±3.17) vs (42.05±3.11),(182.85±6.62) μg/L vs (170.93 ± 6.51) μg/L] were statistically significant compared to the control group [(64.40±4.33) scores vs (53.75±3.73) scores,(3.73± 0.45) scores vs (2.83±0.39) scores,(156.50±5.88) m vs (211.43±7.53) m,(56.80±1.57) mm Hg vs (62.58±1.91) mm Hg,(59.90±3.49) mm Hg vs (55.98±3.36) mm Hg,(38.85±2.77) vs (40.80±3.16),(180.60±5.23) μg/L vs(172.83±5.22) μg/L](all P ＜0.05 or P ＜0.01),the rate of acute exacerbations COPD and hospital days were decreased,and the experimental group excelled.Conclusions Our study indicates that longterm NIPPV could significantly improve the living conditions of the patients with severe stable COPD complicated with respiratory failure,lower the serum levels of MMP-9.