Fetal isolated lung is a congenital malformation of the lung 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. Fetal isolated lung is divided into lobar and intralobar types, with intralobar isolated lung being the rarer type and the majority being lobar. Lobar isolated lung, also known as parapneumonia, is separate from normal lung tissue, has its own pleural envelope, and has a blood supply derived from the body circulation. Most isolated lung occurs at the base of the lung, at the base of the left thoracic cavity, with some occurring 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 use during the mother’s pregnancy. The vast majority of fetal isolated lung has a good prognosis, and some lesions that are not accompanied by other abnormal signs may spontaneously shrink or disappear, but require continuous dynamic follow-up and observation of the fetus. However, if the isolated lung mass is too large and grows too fast, compressing the heart, normal lung, and inferior vena cava, it may cause severe pulmonary dysplasia, heart failure, and fetal edema, etc. The growth rate of the mass and fetal signs should be closely monitored. Pregnant women can continue the pregnancy according to medical advice and wait until the fetus is born for surgical treatment, which can restore normal function. In case of serious conditions during pregnancy, the pregnancy needs to be terminated promptly.