Objective To sum the factors associated with mechanical ventilation assistant difficulty in weaning of mechanical ventilation.Methods Data of 23 patients, in the First Hospital of China Medical University between January 2007 to January 2008,with mechanical ventilation but for difficult weaning were retrospectively analyzed.Results In 23 patients with difficult weaning,there were 6 cases with temperature 38 ℃,12 cases with PaCO2 60 mm Hg,3 cases with psychological dependence on ventilator, and 2 cases with improper time in weaning.Conclusions Timely assess of the patients' symptom,reasonable protective mechanical ventilation, enough nourishment support may reduce incidence of difficult weaning,and enhance achievement ratio of weaning of mechanical ventilation.