Whether radiotherapy is needed after grade III surgery for invasive ductal carcinoma of the breast needs to be decided according to the scope of surgery and axillary lymph node dissection, lymph node metastasis and tumor stage. Invasive ductal carcinoma of the breast refers to cancer cells originating from the epithelium of breast ducts, and the cancer cells break through the basement membrane to infiltrate into the deep layer. Histological grading is based on the degree of glandular duct formation, nuclear polymorphism and nuclear division ability, and it is classified into grade I to III. Grade III is high grade, which suggests that the tumor is poorly differentiated and highly malignant. If breast-conserving surgery is performed for grade III invasive ductal carcinoma of the breast, radiotherapy is recommended to eliminate the possible residual local cancer cells. For total excision surgery, radiotherapy is not needed if there is no lymph node metastasis and the tumor is ≤5cm (T3~4), and radiotherapy is recommended if the tumor is >5cm (T1~2); radiotherapy can be considered for axillary lymph node dissection if there are 1-3 lymph nodes metastasis, and recommended for axillary clearance if there are ≥4 lymph nodes metastasis; radiotherapy is recommended for >1 micro metastasis or 1-2 macro metastasis without axillary clearance. Whether radiotherapy is given after grade III surgery for invasive ductal carcinoma of the breast also needs to consider the general condition of the patient’s body and the willingness to be treated, etc. It is recommended that the patient should consult a specialist for timely consultation and choose the appropriate treatment.