Objective:To analyze the efficacy and safety of nalbuphine for analgesia in patients with non-mechanical ventilation in intensive care unit (ICU).Methods:From December 2018 to August 2021, a multicenter randomized controlled clinical study was conducted to select non-mechanical ventilation patients with analgesic needs admitted to ICU of four hospitals in Henan Province and Guizhou Province. Patients were randomly assigned to nalbuphine group and fentanyl group. The nalbuphine group was given continuous infusion of nalbuphine [0.05~0.20 mg/(kg·h)], and the fentanyl group was given continuous infusion of fentanyl [0.5~2.0 μg/(kg·h)]. The analgesic target was critical-care pain observation tool (CPOT) score<2. The observation time was 48 hours. The primary endpoint was CPOT score, the secondary endpoints were Richmond agitation-sedation score (RASS), ICU length of stay, adverse events, and proportion of mechanical ventilation. The quantitative data of the two groups were compared by t test or Mann-Whitney U test. The enumeration data were compared by chi square test or Fisher exact probability method. The data at different time points between groups were compared by repeated measures analysis of variance. Results:A total of 210 patients were enrolled, including 105 patients in the nalbuphine group and 105 patients in the fentanyl group. There was no significant difference in baseline data between the two groups (all P>0.05). There was no significant difference in CPOT score between nalbuphine group and fentanyl group at each time point after medication ( P>0.05), the CPOT score of both groups at each time point after medication was significantly lower than that before medication, and the analgesic target could be achieved and maintained 2 hours after medication. There was no significant difference in RASS between the two groups at each time point after medication ( P>0.05), which was significantly lower than that before medication, and the target sedative effect was achieved 2 hours after medication. There was no significant difference in ICU length of stay between nalbuphine group and fentanyl group [5.0(4.0,7.5) d vs. 5.0(4.0,8.0) d, P=0.504]. The incidence of delirium, nausea and vomiting, abdominal distension, pruritus, vertigo and other adverse events in the nalbuphine group was lower than that in the fentanyl group (all P<0.05). There was no significant difference in the incidence of other adverse events such as deep sedation, hypotension and bradycardia between the two groups (all P>0.05). The incidence of respiratory depression in nalbuphine group was not significantly different from that in fentanyl group ( P>0.05), but the proportion of mechanical ventilation was significantly lower than that in the fentanyl group [1.9% (2/105) vs. 8.6%(9/105), P=0.030]. Conclusions:Nalbuphine could be used for analgesia in ICU patients with non-mechanical ventilation. The target analgesic effect could be achieved within 2 hours, and it had a certain sedative effect with a low incidence of adverse reactions.