Objective To observe the efficacy and safety of remifentanil in patients with mechanical ventilation in Intensive Care Unit (ICU) .Methods Totally 90 cases were enrolled ,patients with mechanical ventilation were randomly divided into two groups (remifentanil vs .fentanyl) ,45 cases in each group .We used facial expression score (FPS) to monitoring pain ,richmond se‐dation agitation score (RASS) was the sedation tool for measuring quality and depth of sedation .Propofol wase used for sedation therapy .We recorded the data including FPS and RASS and vital signs during the treatment .The primary outcome was the time to reach the goal of analgesia sedation ,cases of using propofol and doses of propofol .The secondory outcome was mechanical ventila‐tion time ,ICU length of stay and adverse events .Results Fentanyl and remifentanil all could achieve the desired analgesic effect . Compared with fentanyl group ,FPS scores showed significantly decreased after 5 min application of remifentanil (P< 0 .05) ,but FPS scores showed significantly decreased after 10 min application of fentanyl .Analgesia goal time of the remifentanil and fentanyl were(5 .00 ± 1 .37)min and (30 .00 ± 4 .50)min ,respectively .Only 28 .9% of the patients should be combined use of propofol in remifentanil group ,but fentanyl group was 64 .4% (P<0 .01);the dosage of propofol of remifentanil group was lower than those of fentanyl group ;there was no significant difference in central venous pressure (CVP) and heart rate(HR) between the two groups at each time point(P>0 .05) .The mechanical ventilation time ,ICU length of stay in the patients with remifentanil were significantly shorter(P<0 .05) ,and adverse events occur less(all P<0 .05) .Conclusion Remifentanil analgesia in patients mechanical ventilated patients is fast onset of action ,analgesic effect significantly ,with less sedative drug dosage .It also can shorten mechanical ventila‐tion time ,ICU length of stay and has no obvious side effects .