Objective To analyze the clinical data of 24 difficult weaning cases by long term mechanical ventilation in intubated chronic obstructive pulmonary disease (COPD),and to investigate the successful weaning factors.Methods 24 COPD patients combined with hypercapnic respiratory failure who received mechanical ventilation over 72 h were divided into two groups.17 patients in group A were successful in weaning,however 7 patients in group B failed.The general condition,intubated and ventilated time,arterial blood gas analysis(ABGs),pulmonary function test and respiratory mechanics were monitored and measured respectively.Results There were no significant difference in ABGs,APACHEⅡ,oxygenation index (OX) and airway resistance(P0.05).There were significant differences in the following parametes between two groups:intubated and mechanical time (6±2)d vs (16±5)d;rapid shallow breath index (RSBI,f/V T),(70±25)times·min -1 ·L -1 vs (110±22)times·min -1 ·L -1 );maximal inspiratory pressure (Pimax),(-22±3)cm H 2O vs (-12±3)cm H 2O;intrinsic positive end expiratory pressure (PEEPi),(6±2)cm H 2O vs (11±3)cm H 2O(P0.05).Conclusion Whether the mechanical ventilator weaning is successful or not for the COPD patients combined with respiratory failure who underwent intubation and long term mechanical ventilation depends on the intubated and ventilated time,the pump function and reserved capacity of respiratory muscles.