Inclusion Criteria:
1. Participants voluntarily join this trial and sign an informed consent form.
2. Newly diagnosed stage III or IV epithelial ovarian cancer, fallopian tube cancer, or primary peritoneal cancer, confirmed by histological or cytological pathology.
3. Prior to first-line platinum-based doublet chemotherapy combined with bevacizumab.
4. No disease progression as assessed by the investigator after completion of first-line platinum-based therapy and before randomization.
5. Participants' homologous recombination deficiency test results must meet the criteria.
6. Participants have not received any anti-tumor therapy from the last dose of first-line platinum-based therapy until randomization.
7. Able to provide sufficient fresh or archived tumor tissue specimens for testing at the sponsor-designated central laboratory.
8. ECOG PS score: 0-1.
9. Expected survival ≥ 12 weeks.
10. Laboratory tests within 7 days prior to randomization confirm that important organ function meets the requirements.
11. Female participants of childbearing potential must have a negative serum human chorionic gonadotropin (HCG) test within 7 days prior to randomization and must not be breastfeeding; female participants of childbearing potential must agree to adhere to contraception from the date of signing the informed consent form until 7 months after the last dose.
Exclusion Criteria:
1. Participants with untreated or active central nervous system (CNS) metastases; a history of meningeal metastases or current meningeal metastases.
2. Participants with clinically symptomatic, poorly controlled, or moderate to severe pleural effusion, pericardial effusion, or ascites.
3. Participants with a history of or concurrent other malignancies, excluding cured basal cell carcinoma of the skin, cervical carcinoma in situ, ductal carcinoma in situ of the breast, papillary thyroid carcinoma, and other malignancies that have been adequately treated and cured for ≥5 years prior to randomization with evidence of no recurrence or metastasis.
4. Participants with a history of interstitial pneumonia/interstitial lung disease requiring steroid treatment, non-infectious pneumonia (such as radiation pneumonitis), current or suspected interstitial pneumonia/interstitial lung disease, non-infectious pneumonia, or other active pneumonia; or those with severe asthma, severe chronic obstructive pulmonary disease (COPD), restrictive lung disease, or other lung damage within 6 months prior to randomization.
5. 6\. Individuals with active pulmonary tuberculosis; those who have received adequate and regular treatment and have stopped anti-tuberculosis treatment for ≥3 months prior to randomization are eligible for enrollment.
7\. Individuals with poorly controlled or severe cardiovascular disease. 8. Individuals who have experienced arterial/venous thrombotic events within 6 months prior to randomization.
9\. Individuals who have experienced NCI-CTCAE v6.0 grade ≥2 bleeding events within 1 month prior to randomization.
10\. Individuals with known hereditary or acquired bleeding (e.g., coagulation disorders) or thrombotic tendency.
11\. Individuals who have experienced or are expected to experience gastrointestinal perforation or fistula, tracheal fistula, urethral fistula, or abdominal abscess in the near future.
12\. Individuals with gastrointestinal obstruction or symptoms and signs of gastrointestinal obstruction within 3 months prior to randomization; individuals who have previously undergone intestinal stent implantation and whose intestinal stent has not been removed by the screening period.
13\. Participants who have experienced severe infection within 1 month prior to randomization.
14\. Participants who have tested positive for human immunodeficiency virus (HIV); participants with known active hepatitis.
15\. Participants who have undergone major surgery within 4 weeks prior to randomization or whose surgical side effects have not recovered or stabilized prior to randomization. 16. Patients who may receive other systemic anti-tumor therapies during treatment or are scheduled for further debulking surgery.
17\. Patients whose toxicity from previous anti-tumor therapy has not recovered to grade ≤1 according to the NCI-CTCAE v6.0 classification.
18\. Patients with known hypersensitivity to any component of the SHR-A1811 product or other monoclonal antibody drugs.
19\. Patients who, in the investigator's judgment, have other factors that may affect the trial results or force the trial to be terminated midway, such as alcoholism, drug abuse, substance abuse, criminal detention, etc., as well as other serious illnesses (including mental illness) requiring concomitant treatment, serious abnormal laboratory test results, or any other circumstances that may increase the risk of participation in the trial, interfere with the trial results, or make them unsuitable for participation in the trial.
