Objective To explore the early effectiveness of arthroscopic tri-anchor double-pulley suture-bridge in treatment of medium-size supraspinatus tendon tears. Methods Between December 2020 and January 2023, 40 patients with medium-size supraspinatus tendon tears were treated with arthroscopic tri-anchor double-pulley suture-bridge. There were 18 males and 22 females, with an average age of 62.6 years (mean, 45-73 years). Among them, 17 patients had trauma history. The main clinical symptom was shoulder pain with hug resistance test (+). The interval from symptom onset to operation was 10.7 months on average (range, 3-36 months). Visual analogue scale (VAS) score, University of California Los Angeles (UCLA) score, American Shoulder and Elbow Surgeons (ASES) score, and shoulder range of motion (ROM) of forward flexion, abduction, and external rotation were used to evaluate shoulder function. MRI was performed to assess the structural integrity and tension of reattached tendon. Patient satisfactions were calculated at last follow-up. Results All incisions healed by first intention, no complications such as incision infection or nerve injury occurred. All patients were followed up 12-37 months (mean, 18.2 months). At 12 months after operation, VAS score, UCLA score, and ASES score significantly improved when compared with the preoperative scores (P<0.05). At 3 and 12 months after operation, the ROM of external rotation significantly improved when compared with preoperative one (P<0.05), and further improved at 12 months after operation (P<0.05). However, the ROMs of abduction and forward flexion did not improve at 3 months after operation when compared with those before operation (P>0.05), but significantly improved at 12 months after operation (P<0.05). Twenty-six patients underwent MRI at 3-6 months, of which 23 patients possessed intact structural integrity, good tendon tension, and tendon healing; 3 patients underwent tendon re-tear. The self-rated satisfaction rate was 92.5% at last follow-up. Conclusion Arthroscopic tri-anchor double-pulley suture-bridge in treatment of medium-size supraspinatus tendon tears can maximize the tendon-bone contact area, obtain satisfied early effectiveness with high satisfaction rate and low incidence of tendon re-tear. However, the function of abduction is limited at 3 months after operation, and patients need to adhere to rehabilitation training to further improve the joint activity.