Objective:To compare the advantages of nano carbon suspension mapping method and non dye method in the number of axillary lymph nodes detected during axillary lymph node dissection and axillary micro lymph nodes detected after neoadjuvant chemotherapy for breast cancer.Methods:From January 1st, 2018 to July 1st, 2018, 66 breast cancer patients who were to undergo axillary lymph node dissection after new adjuvant treatment were selected for the prospective study.Using the method of random number table, the patients were randomly divided into two groups: the group of nano carbon mapping (33 cases) and the control group (33 cases). After 24 hours subcutaneous injection of nano carbon before operation, axillary lymph node dissection and direct axillary lymph node dissection without dye were used.The number of axillary lymph nodes and the number of micro axillary lymph nodes in the two groups were observed.Results:The number of axillary lymph nodes and micro lymph nodes in the nano carbon mapping group were higher than those in the control group.The differences were statistically significant (the number of axillary lymph nodes were (19.3±6.2) vs (14.9±6.7), P=0.007; the number of micro-lymph nodes were 2.0(0.5, 3.0) vs 0(0, 1.0), Z=-4.328, P<0.001). Conclusion:Nano carbon suspension mapping can increase the number of lymph nodes detected in axillary lymph node dissection after neoadjuvant chemotherapy for breast cancer, and also has advantages in the detection of some small axillary lymph nodes that are not easy to find.