Fetal isolated lung, which has a low incidence, is a congenital malformation of the lungs in which part of the lung tissue is separated from normal lung tissue and the isolated lung may not be connected to the normal lung. Isolated lungs are categorized into lobar and intralobar types. Fetal intralobar isolated lungs are rare, and most are lobar. Lobular isolation lungs, also known as collateral lungs, are separate from normal lung tissue, have their own pleural envelope, and derive their blood supply from the body’s circulation. Most isolated lungs occur at the base of the lungs, at the base of the left thoracic cavity, and some occur in the mediastinum, diaphragm, subdiaphragm, or pericardium. The cause of fetal isolated lung is not well understood and may be related to conditions such as malnutrition, alcoholism, smoking, and drug abuse during the mother’s pregnancy. The vast majority of fetal isolated lungs have a favorable prognosis, and some of the lesions that are not accompanied by other abnormal signs may shrink or disappear spontaneously, but continuous dynamic follow-up observation of the fetus is required. However, if the isolation lung mass is too large and grows too fast, compressing the heart, normal lungs and inferior vena cava, etc., it may cause severe pulmonary hypoplasia, heart failure and fetal edema, etc. The growth rate of the mass and fetal signs should be closely observed. Pregnant women can follow the doctor’s advice to continue the pregnancy and wait until the fetus is born and surgical treatment can restore normal function. In case of serious conditions during pregnancy, timely termination of pregnancy is required.