To explore the application effect of ultrasound combined with magnetic resonance imaging (MRI)for diagnosing monochorionic multiple pregnancy malformations. Methods: The clinical data of 86 pregnant women with suspected monochorionic multiple pregnancy malformations between January 2017 and September 2021 were collected retrospectively. These women had received ultrasound and MRI examinations. The results of delivery, odinopoeia, or surgery of the women were used as the gold standards, the application effect of ultrasound, MRI, and the ultrasound combined with MRI for diagnosing the monochorionic multiple pregnancy malformations were evaluated . Results: 28 of 86 pregnant women were diagnosed as monochorionic multiple pregnancy malformations. Based on the gold standard of diagnosis, the Kappa values of ultrasound, MRI, and ultrasound combined with MRI for diagnosing the monochorionic multiple pregnancy malformations were 0.716, 0.726, and 0.747, respectively. The sensitivity, the specificity, the accuracy rate, the positive prediction value, and the negative prediction value of ultrasound for diagnosing monochorionic multiple pregnancy malformations were 75.0%, 89.7%, 84.9%, 77. 8%, and 88.1%, respectively, which of MRI for diagnosing monochorionic multiple pregnancy malformations were 89.3%, 84.5%, 86.1%, 73.5%, and 94.2%, respectively, and which ultrasound combined with MRI for diagnosing the monochorionic multiple pregnancy malformations were 92.9%, 84.5%, 87.21%, 74.3%, and 96.1%, respectively. Conclusion: Ultrasound, MRI, and ultrasound combined with MRI for diagnosing the monochorionic multiple pregnancy malformations have the same good consistency. Ultrasound combined with MRI has better diagnostic value, which is of great significance for clinical intervention, taking effective measures, and reducing the rate of adverse pregnancy, with the increased sensitivity and negative predictive value of malformation diagnosis.