The goal of this clinical trial is to learn if Oliceridine fumarate injection works to treat acute pain after abdominal surgery. It will also learn about the safety of Oliceridine fumarate injection. The main questions it aims to answer are:

1. Does Oliceridine fumarate injection works to treat acute pain after abdominal surgery?
2. Does Oliceridine fumarate injection lead to less adverse effect?

Researchers will compare Oliceridine fumarate injection to a positive-drug (Sufentanil Citrate) to see if Oliceridine fumarate injection not inferior to sufentanil in the efficacy and safety for acute pain after abdominal surgery.

Participants will:

1. Receive patient controlled analgesia treat using Oliceridine or sufentanil after surgery
2. Be followed up every 6 hours until 48 hours after surgery or before discharge

Traditional opioid, such as morphine, sufentanil , is an important drug treatment of postoperative period of acute pain, but their use is often limited because of significant side effects, such as respiratory depression, postoperative nausea and vomiting and sedation. If a drug is effective treatment of postoperative pain and avoid these adverse reactions, it will shorten the postoperative recovery time of patients, increase patients' satisfaction, and reduce hospitalization costs. Basic research shows that traditional opioids mainly bind to μ-opioid receptors and activate G protein signal transduction to exert analgesic effect. In addition, they stimulate the recruitment of β-arrestin, leading to respiratory depression, nausea and vomiting and other side effects. Oliceridine is a newly μ-opioid receptor agonist, which mainly activates the G protein signaling pathway to exert analgesic effect, but has a weak recruitment effect on β-arrestin and thus reduces the incidence of adverse reactions. However, due to its recent introduction to the market, there is still a lack of large-scale clinical studies on the application of Oliceridine in the population. So this topic to discuss the analgesic efficacy and adverse reactions of Oliceridine in patients with acute pain after abdominal surgery. Our study hypothesized that Oliceridine would have comparable analgesic efficacy and a lower incidence of associated side effects than sufentanil.

Inclusion Criteria:

1.Preoperative inclusion criteria

1. aged ≥18 years and ≤75 years at screening;
2. Plan to undergo open or laparoscopic abdominal surgery, and the estimated operative time more than 2 hours.
3. able to understand and comply with research procedures and requirements, and can provide a written informed consent.

2.postoperative inclusion criteria:

1. patients who required open or laparoscopic surgery;
2. According to the investigator's judgment, the patient had recovered sufficiently from the intraoperative anesthesia protocol to accurately complete the protocol-specified questionnaire;

Exclusion Criteria:

1.preoperative exclusion criteria:

1. ASA grade >III
2. existing other acute or chronic pain conditions;
3. body mass index (BMI) < 18 or > 30 kg/m2;
4. with sleep apnea syndrome; 5 ) long-term opioid treatment, defined as receiving more than 15mg morphine equivalent units per day on more than 3 days per week for a period of more than 1 month in the 12 months prior to surgery;

6) suffering from mental or nervous system diseases (such as epilepsy, depression, schizophrenia, etc.), chronic obstructive pulmonary disease or pulmonary heart disease, heart failure, severe arrhythmia, etc; 7) with severe liver and kidney dysfunction; 8) Other conditions considered by the investigator to be inappropriate for enrollment.

Postoperative exclusion criteria:

1. intraoperative, postoperative or anesthetic deviations that may affect the efficacy and safety evaluation in the study;
2. evidence of hemodynamic instability or respiratory insufficiency.