Ovarian cancer is one of the most dangerous and leading gynecological cancer, with significant cancer-related mortality among women. However, current detection methods are still limited, with approximately 70% of patients with high-grade serous ovarian cancer often being advanced at the initial diagnosis and more than 80% with intraperitoneal spread. The five-year survival rate for late detection is only 29%; on the contrary, if detected early, the five-year survival rate can reach 92%. Therefore, early diagnosis and detection are essential in diagnosing and treating ovarian cancer. Liquid biopsy has attracted widespread attention because of its non-invasive, real-time, and dynamic characteristics. Cell-free DNA in plasma can identify a small tumor burden well and reflect the clinical cancer information of cells.The role of hypermethylation in developing malignant tumors has received increasing attention. Methylation is one of epigenetics and plays a vital role in the occurrence and development of tumors. According to previous research basis of the researchers, it has been found that CDO1 and HOXA9 genes show hypermethylation in ovarian cancer, and they are considered one of the biomarkers for detection. Therefore, this study will further explore the detection of CDO1 and HOXA9 methylation levels based on cell-free DNA in blood and compared with ovarian pathology results; the application of methylation detection technology in ovarian cancer/precancerous lesions will further explore the application value of non-invasive diagnosis and prognostic follow-up.This study will involve three centers and is expected to enroll more than 1,400 clinical subjects, further examine the consistency of methylation detection kits with the histopathological examination, ROMA index, and Sanger sequencing results, and obtain sensitivity and specificity technical performance parameters.