Background This study aims to put forward a new classification of breast asymmetry based on the relative position of the nipple and inframammary fold (IMF) and propose a surgical algorithm of determining new IMF to address breast asymmetry in patients undergoing transaxillary augmentation mammaplasty, which is named as NIMF (nipple inframammary) classification and surgical algorithm. Methods Three hundred and forty-five patients received transaxillary augmentation mammaplasty with anatomical implants. Preoperative breast asymmetry was classified into four types. I: asymmetrical nipple with asymmetrical IMF in the same direction; II: symmetrical nipple with asymmetrical IMF; III: asymmetrical nipple with symmetrical IMF; IV: asymmetrical nipple with unapparent IMF. Surgical plans (3 plans for type I, II, IV while 5 plans for type III) to set the new IMF were provided for each patient, who chose one of them as the final surgical plan. Breast-Q and Likert scale were used to evaluate patient satisfaction and symmetry of breast preoperatively and 6 months postoperatively. Results The incidence of type I, II, III, IV was 30%, 15%, 13%, and 4%, respectively. Ninety-seven percent of patients with breast asymmetry chose plan C, which aimed to balance the relative position of nipple and IMF. Postoperative Breast-Q scores showed a significant rise compared with preoperative scores, but no statistical difference between plan C V.S. other plans. Patients with symmetrical preoperative breasts (Group A) had significantly higher postoperative Breast-Q scores than patients with asymmetrical preoperative breasts (Group B). In breast symmetry assessment, Group A had a significantly higher postoperative score than Group B, but the postoperative score was significantly lowered compared with the preoperative score in both Group A and B. Conclusion The NIMF classification and surgical algorithm provide a systematic and scientific way to analyze and improve breast asymmetry, to achieve optimized patient satisfaction in transaxillary augmentation mammaplasty with anatomical implants.