Objective:To observe the clinical effect of high suspension and low incision (HSLI) surgery on mixed haemorrhoids,compared with Milligan-Morgan haemorrhoidectomy.Methods:A multi-centre,randomized,single-blind,non-inferiority clinical trial was performed.Participants with mixed haemorrhoids from Xiyuan Hospital of China Academy of Chinese Medical Sciences,Beijing Rectum Hospital,Air Force Medical Center of People\'s Liberation Army of China,and Puyang Hospital of Traditional Chinese Medicine were enrolled from September 2016 to March 2018.By using a blocked randomization scheme,participants were assigned to two groups.The experimental group was treated with HSLI,while the control group was treated with Milligan-Morgan haemorrhoidectomy.The primary outcome was the clinical effect evaluated at 12 weeks after operation.The secondary outcomes included the number of haemorrhoids treated during the operation,pain scores,use of analgesics,postoperative oedema,wound healing,incidence of anal stenosis,anorectal manometry after operation,as well as surgical duration,length of stay and total hospitalization expenses.A safety evaluation was also conducted.Results:In total,246 eligible participants were enrolled,with 123 cases in each group.There was no significant difference in the clinical effect between the two groups (100.00％ vs.99.19％,P＞0.05).Compared with the control group,the number of extemal haemorrhoids treated during the operation and the pain scores after operation were significantly reduced in the experimental group(P＜0.05 or P＜0.01);the patient number with wound healing at 2 weeks after operation and the functional length of anal canal at 12 weeks after operation were significantly increased in the experimental group (P＜0.05).There was no significant difference in the incidence of anal stenosis,the numbers of patients using analgesics and patients with postoperative oedema between the two groups after operation (P＞0.05).The surgical duration and length of stay in the experimental group were significantly longer than those in the control group,and the total hospitalization expense was significantly higher than that in the control group(all P＜0.05).No adverse events were reported in either group during the whole trial or follow-up period.Conclusion:HSLI had the advantages of preserving the skin of anal canal completely,alleviating postsurgical pain and promoting rapid recovery after operation.(Registration No.ChiCTR1900022883)