Abstract： Objective To investigate the effects of work of breathing ventilation and Ti/Ttot in the weaning process for patients undergoing mechanical ventilation. Method A prospective analysis was conducted. Eighty-six mechanically ventilated patients, who were admitted for weaning in the intensive care unit from Jan. 2007 to Jan. 2008 were enrolled. The patients in the trial all fulfilled the criteria of discontinuing ventilation and ventilation time no less than 72 hours. According to the diagnosis, they were divided into 2 groups (COPD group and acute toxicoais group). Furthermore according to the outcome of weaning from mechanical ventilation, patients were divided into a failure group and a success group. T-test, chi-square test and logistic regression were used for statistics analysis. Results The results of WOB between the failure group and the success group were approximate to the accepted level(WOB < 0.75 J/L). But there were significant differences on heart rate, ventilation time, WOB and Ti/Ttot between two groups (P <0.05). The logistic regression indicated that the WOB and Ti/Ttot were valuable to pre-dict weaning of ventilator(both OR> 1). Conclusions The parameter of WOB and Ti/Ttot might had a useful ef-fect on weaning of ventilator, but as a supplement it could not evaluate completely by itself, It also needed to com-bine with other parameters. Meanwhile the experience of the duty doctors also had important effects on weaning.