The hard lump pain in the left breast of a 7 and a half year old girl can be considered to be caused by prepubertal breast development, bacterial infection and precocious puberty. 1. Pre-pubertal breast development: the etiology is not clear, mostly belongs to the estrogen abnormality. The main manifestation of unilateral breast visible lumps, not usually need to do special treatment, more to be observed, usually pay attention to diet, to avoid eating foods containing estrogen, such as fried foods. 2. Bacterial infection: most of the bacteria invade the breast because of not dealing with local hygiene, plus clothing and other friction, resulting in lumps and pain. The main treatment is medication, using penicillin and other antibiotics for treatment. 3. Precocious puberty: Mostly due to dietary reasons, excessive intake of food or drugs containing estrogen. It is often characterized by early breast development, menstruation and breast lumps. In addition to dietary management, medication can be used, such as medroxyprogesterone. In addition, breast trauma and breast tumors may also present similar clinical manifestations. 7 and a half year old girls with hard lump pain in the left breast should consult a doctor in time for a professional examination and follow medical advice.