Methylmalonic aciduria is the most common organic acid metabolic disease, which can develop from the neonatal period to the adult period, and is mainly characterized by neurological damage, renal damage, visual damage and other multi-system damage in childhood. The clinical symptoms of pulmonary hypertension lack specificity and are insidious, and the early symptoms are not obvious, so they are not easily noticed by parents and doctors, such as fast breathing, fast heart rate, insidious cyanosis, etc. Once pulmonary hypertension appears in this disease, it progresses rapidly and can cause severe heart failure within a few months, which endangers the life of the child. This is a miracle in the field of treatment of pulmonary hypertension, and we have successfully treated several cases of children with this disease. Therefore, children with methylmalonic aciduria should routinely undergo echocardiography to monitor pulmonary artery pressure, and if a significant increase in pulmonary artery pressure is found, further investigation and treatment should be performed. Conversely, in children with a clinical diagnosis of idiopathic pulmonary hypertension and other unexplained pulmonary hypertension, attention should be paid to the exclusion of methylmalonic aciduria as a treatable disease and to the presence of clinical manifestations of multisystem damage. If the blood homocysteine level is significantly elevated, blood and urine tests for amino acids and organic acids should be performed in a timely manner to clarify the cause and avoid missed diagnosis.