This study is a randomized, double-blind, placebo-controlled, parallel-group clinical trial. To preliminarily evaluate the safety and efficacy of KHN702 tablets in moderate to severe post-operative pain patients.

Inclusion Criteria:

1. Subjects between the ages of 18 and 75 years, inclusive.
2. Body mass index (BMI) of 18.0 to 30.0 kg/m2, inclusive.
3. Patients scheduled for surgery.
4. According to the researcher's medical judgment, American Society of Anesthesiologists (ASA) classification≤Grade II.
5. The subject can understand and comply with the study procedures and requirements, and can provide written informed consent prior to any study procedures.
6. NRS ≥ 4 points within 6 hours after surgery.

Exclusion Criteria:

1. Participants experiencing acute or chronic pain unrelated to the surgical site, which the investigator deems may confound the participant's assessment of postoperative pain.

2. History or evidence of any of the following conditions prior to screening:

   • History of significant cardiovascular or cerebrovascular disease;
   • Severe respiratory disease history;
   • Severe Neurological and Psychiatric disease History;
   • Active peptic ulcer disease, significant vomiting, chronic diarrhea, ileus, malabsorption, or other known conditions that significantly affect drug absorption, distribution, metabolism, or excretion;
   • Subjects at high risk of bleeding who are deemed unsuitable for this trial by the investigator;

3. Long-term use of opioids or nonsteroidal anti-inflammatory drugs within the past 30 days prior to screening, or discontinuation of medications affecting analgesic efficacy assessment (except those permitted by the protocol) less than 5 half-life prior to randomization.

4. Subjects with a history of opioid allergy, or those with a history of allergy to the intraoperative medications specified in the protocol, postoperative rescue analgesics, or known allergies to the investigational drug or its excipients.

5. Subjects who underwent major surgery within 3 months prior to screening and the investigator determined that it would affect postoperative pain assessment.

6. Any of the following infectious diseases were present during screening: Hepatitis B surface antigen (HBsAg) positive, hepatitis C virus antibody (HCV Ab) positive, human immunodeficiency virus antibody (HIV Ab) positive, or serum treponema pallidum antibody (TPAb) positive.

7. History of substance abuse or alcohol abuse within the three months prior to screening .

8. History of blood donation within the past three months prior to screening.

9. Individuals who have participated in any clinical research within the past three months prior to screening .

10. Pregnant or lactating women; women or men of reproductive potential who are unwilling to use contraception throughout the study period; or subjects (including male subjects) planning to conceive within 3 months after study completion.

11. Subjects with intraoperative blood loss exceeding 1000 mL or those experiencing other severe complications during surgery;

12. Subjects requiring intensive care following surgery;

13. Other circumstances deemed unsuitable for participation in this trial by the investigator.