Critically ill patients need reasonable and moderate analgesic and sedative treatment to eliminate or reduce pain, anxiety and restlessness, improve patient comfort and cooperation, reduce patients' stress response, protect organ function and optimize prognosis. As a semi-synthetic opioid receptor agonist-antagonist, nalbuphine can bind to μ, κand δ receptors, has partial antagonistic effect on μ receptor, and is fully activated on κreceptor, with very weak δ receptor activity. Results of a study on the efficacy and safety of nalbuphine for analgesia in ICU patients showed that nalbuphine has sustained and stable analgesic effect for patients with mild to moderate analgesic needs in ICU, the onset time is comparable to sufentanil, and excessive sedation caused by sufentanil can be avoided, and the effect on hemodynamics is small. It can be used as a new choice of analgesic drugs in ICU. A single-center, randomized, single-blind, prospective study was designed to compare nalbuphine and sufentanil in patients with ARDS after surgery. Sixty patients with ARDS after surgery to be admitted to ICU were randomly divided into experimental group (Nalbuphine group) and control group (Sufentanil group). This study aims to determine the analgesic efficacy and safety of nalbuphine hydrochloride in patients with Acute Respiratory distress syndrome (ARDS) after surgery. The successful development of this study will provide more theoretical basis for the individualized analgesic sedation program for surgical patients.