Objective: To compare the diagnostic value of ovarian-adnexal reporting and data system (O-RADS) and risk of malignant index (RMI) for ovarian tumors, and to explore the independent factors for prediction of malignant ovarian tumors. Methods: Ultrasonographic data of 431 patients with ovarian tumors confirmed by pathology were analyzed retrospectively, and were classified using O-RADS, RMI respectively. Taking the pathological results as the gold standard, the receiver operating characteristic curve (ROC) was performed to calculate the sensitivity, specificity, accuracy and Youden index of O-RADS, RMI. The factors involved in the two methods were analyzed by single and multiple Logistic regression analysis to identify the predictive factors for malignant ovarian tumors. Results: ①431 cases of ovarian tumors were benign and malignant (including borderline). The age，the number for postmenopausal cases, the platelet ,the serum CA125 level and the serum HE4 level in benign group were significantly lower than those in malignant group (P < 0.001).②The sensitivity of O-RADS and RMI in the diagnosis of benign and malignant ovarian tumors was 93.1% and 68.2%, the specificity was 89.5% and 91.9%, the accuracy was 91.0% and 82.4%, and the ROC was 0.94,0.80 respectively. The sensitivity and accuracy of O-RADS was higher than of RMI (P < 0.001), while the AUC ang specificity of 2 methods were no significant difference (P > 0.05). ③Single factors analysis showed that differences of maximum diameter of tumor, thickness of cyst wall or septum, solid component of tumor, papillary projection or nodule, color score and ascites were statistically significant between benign group and malignant group (P < 0.001). Multivariate analysis showed that maximum diameter, thickness of cyst wall or septum (≥ 3cm), solid component of tumor, color score (3-4) and ascites were independent risk factors for ovarian malignant tumor (P < 0.001). Conclusion: O-RADS has high sensitivity than RMI in differentiating benign and malignant ovarian tumors, and has certain clinical value. The maximum diameter of the tumor, thick wall septum (≥ 3cm), solid components of tumor, color score (3-4) and ascites are independent risk factors for predicting ovarian malignant tumors.