Objective To explore the clinical value of ultrasound (US) combined with magnetic resonance imaging (MRI) in the diagnosis of primary small ovarian cancer. Methods Seventy patients with primary small ovarian cancer were selected as study subjects. US and MRI were performed before operation. With postoperative pathological results as the golden standard, the clinical records and imaging data of the patients were included in the study and were analyzed. Results The total MRI×US accuracy rate in the diagnosis of all pathological types in 70 patients (94.29%) was significantly higher than that of US (70.00%) and MRI (81.43%) (P<0.05). US showed that most of the tumors were cystic, cystic wall and septum were uneven in thickness, greater omental were irregular thickened with nodular changes. The colorful blood flow signal mainly was grade III. There was high speed and low resistance artery blood flow in the masses with colorful blood flow, most of which were distributed in the parenchyma, and the distribution of blood vessels was strip, dendritic, mass and in other forms. MRI showed that the tumors were mostly cystic masses or cystic solid masses, the wall was smooth, and the tumor diameter was 44.9-365.7mm, MRI plain scan showed low signal or low and equal signal on T1WI, high or slightly high signal on T2WI. The signal was not uniform, manifesting as mixed signal. There was inhomogeneous high and low mixed signal on DWI. Dynamic contrast-enhanced scan showed that there were uneven thickness of the cystic wall and patchy shadows in cysts, cystic wall, septum and nodules were obviously enhanced, and the solid parts were enhanced obviously. Conclusion The accuracy rate of US combined with MRI in the diagnosis of primary small ovarian cancer is high, and imaging features of the two are obvious, and complement each other. The combined diagnosis is of great reference value in the prevention and treatment of primary small ovarian cancer.