Objective To investigate the prethrombotic state and effect of anticoagulation therapy in patients with chronic obstructive pulmonary disease(COPD) and ventilator-associated pneumonia (VAP)．Methods Forty-six COPD patients were divided into VAP group(25 cases)and non-VAP group (21 cases)．The VAP group were randomly subdivided into two groups：group A(conventional therapy group，n=13)，group B(conventional therapy+anticoagulation therapy group，n=12)．The D-dimer (DD)，fibfinogen(FIB)，pulmonary artery pressure(PAP)and the time of weaning were compared between these groups．Results In the COPD patients，the levels of DD，FIB and PAP were significantly increased in VAP group compared with non-VAP group[(0．50±0．26)mg／L，(3．67 ±0．88) L，(31．71 ± 5．66)mm Hg vs(0．23±0．12)mg／L，(1．56±0．45) L，(15．28 ±2．84)mm Hg，respectively，all Plt; 0．05]．In the COPD patients with VAP，the levels of DD，the content of FIB，PAP and mortality were significantly lower in group B with shorter time of weaning compared with group A[(0．22±0．16)mg／L， (1．56±1．17)g／L，(16．00±2．48)him Hg，8．33％ and(4．00±1．41)d vs(O／41±0．09)mg／L，(3．66± 1．03) L，(28．00±0．85)mm Hg，15．4％ and(10．76±3．35)d，respectively，all Plt;0．05]． Conclusions Prethrombotic state exists in COPD patients with VAP．Aggressive anticoagulation on base of routine therapy，by ameliorating microcireulation，call shorten the time of weaning and reduce the mortalit in these patient