This is a 2:1 randomized, double-blind, placebo-controlled, multi-center, phase III clinical study evaluating the efficacy and safety of ZL-2306 (niraparib) for maintenance treatment in patients with platinum-sensitive relapsed ovarian cancer, fallopian tube carcinoma or primary peritoneal cancer (collectively referred to as relapsed ovarian cancer).The evaluation will be divided into two stages: Stage I will be conducted in all patients, and if the predetermined statistically significant difference is not reached, the trial will continue to extend to Stage II during which evaluation will be performed in gBRCA mutation-positive ovarian cancer patients.

Inclusion Criteria:

• Aged 18 years or older female.
• High-grade serous or dominantly high-grade serous ovarian cancer
• The subject shall have received two lines of platinum-containing chemotherapy, complete response [CR] or partial response [PR] after first-line platinum-containing chemotherapy, and after received at least 4 cycles of platinum-containing (must be carboplatin or cisplatin or nedaplatin) in second-line platinum-containing chemotherapy.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

Exclusion Criteria:

• Patients who have undergone ascites drainage with the last two cycles of the last chemotherapy regimen prior to enrollment.
• Symptomatic brain metastases or leptomeningeal metastases that have not been controlled.
• Patients who have been diagnosed previously or currently with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML).