Left breast occupancy is an ultrasound presentation of cystic lesions and solid masses in the breast tissue. If the cyst is small and has no obvious changes, it can be observed and followed up. If the cyst is large, it needs to be treated surgically or punctured to obtain cystic fluid for examination. Benign tumors are usually found in breast fibroadenoma, which is more common in young women, with smooth tumors and good mobility, and the fundamental treatment is surgery. The performance of malignant tumor can have no obvious symptoms in early stage, and small painless single lumps can be found, which are hard, not smooth on the surface, not easily demarcated from the surrounding tissues, and not easily pushed in the breast, which can be initially judged by ultrasound examination, and eventually the pathological examination is the gold standard. The mere description of breast occupancy does not determine the specific disease and further examination is required.