Objective: To analyze application of expansive water separation technique in ultrasound-guided minimally invasive rotary resection of benign breast tumor and its influences on serum inflammatory factors. Methods: A total of 492 patients with benign breast tumors undergoing ultrasound-guided minimally invasive rotary resection were enrolled. According to different local anesthesia methods, they were divided into traditional infiltration anesthesia group (n=234, traditional local infiltration anesthesia) and expansive water separation group (n=258, expansive water separation technique). The perioperative indexes (operation time, intraoperative blood loss, anesthesia time, length of hospital stay), scores of visual analogue scale (VAS), levels of serum interleukin (IL)-6, IL-10, C-reactive protein (CRP) and tumor necrosis factor-α (TNF-α) were compared between the two groups. The occurrence of complications and score of Vancouver scar scale (VSS) were recorded. Results: Compared with traditional infiltration anesthesia group, operation time was shorter (P<0.05), intraoperative VAS score was lower (P<0.05), and anesthesia time was longer in expansive water separation group (P<0.05). At 3 d after surgery, levels of serum IL-6, IL-10, CRP and TNF-α in expansive water separation group were lower than those in traditional infiltration anesthesia group (P<0.05). The incidence of complications in expansive water separation group was lower than that in traditional infiltration anesthesia group (P<0.05). At 6 months after surgery, VSS scores in expansive water separation group were lower than those in traditional infiltration anesthesia group (P<0.05). Conclusion: The application of expansive water separation technique in ultrasound-guided minimally invasive rotary resection of benign breast tumor can shorten operation time, relieve intraoperative pain, inhibit inflammatory response, improve breast aesthetics and reduce complications.