Introduction Idiopathic hyper eosinophilic syndrome (HES) is a rare disease characterized by sustained increase in eosinophilia. Lesions can affect various organs and systems. The global prevalence rate is unknown, and the prognosis is poor. At present, most of the literature reports are based on cases. Heart involvement may be present in 50% to 60% of patients, this is called Loffler endocarditis. Loffler endocarditis is a serious complication of hyper eosinophilia syndrome, which is characterized by a special type of fibrotic endocarditis. Loffler endocarditis is an inflammatory cardiac condition characterized by eosinophilic infiltration in the heart. Methods In this article we report an 8-year-old girl who was diagnosed as having Loffler endocarditis in thrombotic phase and treated by surgery successfully. Results Our patient had a good prognosis during the follow up of half year. She had no symptoms of heart failure and echocardiography findings were normal. Discussion The cardiac damage occurs in three stage processes: the necrotic, thrombotic, and fibrotic stages. This unusual but sometimes life-threatening disease is often detected in the late phase, resulting in no curative strategy available to reverse the disease process. The overall prognosis of patients with Loffler endocarditis is very poor. Current treatments include anticoagulation and anti-eosinophils therapy，surgery only used in selected cases. Surgical treatment of HES in adolescents is very rare. The present case illustrates that with well controlled peripheral eosinophilia, proper surgical treatment in selected patients can improve their prognosis in the near future but long-term follow up is necessary.