Analysis: Hemangioma is a kind of benign tumor composed of newborn blood vessels, most scholars believe that it is a human embryonic development process, especially in the early stage of vascular tissue differentiation, due to the control of the gene segment appeared in a small range of misconfiguration and lead to the specific part of the tissue differentiation abnormality, and the development of hemangiomas, 80% of which are congenital, and most of them occur in the infants and young children stage. They can be classified as nevus erythematosus, capillary hemangioma, cavernous hemangioma, and mixed. They are benign tumors that grow slowly and rarely become malignant. This case is a congenital intramuscular cavernous hemangioma, which invaded the flounder muscle of the lower leg, and the tumor continued to expand and increase in size in all directions, invading the surrounding adjacent tissues, forming a huge hemangioma of the affected limb, and causing deformity of the affected limb. It is rare to find such an “elephant leg” in the fetus of a pregnant woman at 26+6 weeks of pregnancy. This case gives us the message that we should always perform obstetric checkups on time during pregnancy, and three-dimensional ultrasound examination is essential, especially for pregnant women older than 35 years old, who should be carefully screened.