Objective To investigate the value of preoperative axillary ultrasound combined with methylene blue tracer to show lymphatic drainage in sentinel lymph node biopsy (SLNB) of breast cancer patients with clinically negative axillary lymph nodes.Methods From April 2015 to March 2019, breast cancer patients with clinically negative axillary lymph nodes (n=36) were selected as observation group, and were treated with SLNB by methylene blue staining method and axillary ultrasound before operation to mark lymph nodes at low level and near the breast; the intraoperative sentinel lymph node location and pathological Results were analyzed.Another 36 breast cancer patients were selected as control group during the same period to perform SLNB by methylene blue staining method, and no lymph node ultrasound analysis and body surface labeling were performed before the operation.The detection rate, accuracy, specificity, and sensitivity between the two groups were compared.Results The detection rate of sentinel lymph node in the observation group (97.22%) was higher than that in the control group (72.22%) (P<0.05).The accuracy, sensitivity, and specificity of axillary lymph nodes detected by preoperative axillary ultrasound combined with methylene blue were 94.44%, 96.43%, and 77.78%, respectively.Conclusion Preoperative axillary ultrasound can locate the sentinel lymph nodes, accurately determine the status of axillary lymph node metastasis in breast cancer, reduce the defect of partial absence of blue staining with methylene blue tracer alone, and reduce the incidence of false negative, which is suitable for promotion and application in primary hospitals.