In order to investigate the relationship between the extent of tumor invasion and the tumor size, axillary lymph nodes metastasis, Her-2 gene overexpression, and histologic grading in breast invasive ductal carcinoma as well as the optimal extent of excision during the breast-serving surgery, the clinical data of 104 patients with breast invasive ductal carcinoma who had received modified radical mastectomy were analyzed. The correlation analysis on invasive extent, which was evaluated by serial sections at an interval of 0.5 cm from 4 different directions taking the focus as the centre, and the tumor size, axillary lymph nodes metastasis, Her-2 gene overexpression, and histologic grading was processed. There was a significant correlation between invasive extent and tumor size (r=0.766, P<0.01), and lymph nodes metastases (r=0.574, P<0.01), but there was no significant correlation between invasive extent and Her-2 expression (r=0.106, P>0.05), and histologic grading (r=0.228, P>0.05). The 100% negative rate of infiltration in patients without nipple discharge with tumor size <2, 2-3 and >3 cm was obtained at 1.5, 2.0 and 2.5 cm away from the tumor respectively. It is concluded that the performance of breast-serving surgery in patients with breast invasive ductal carcinoma should be evaluated by tumor size in combination with axillary lymph nodes involvement to decide the possibility of breast-serving and the secure excision extent.