Objective To compare the effectiveness of the long head of the biceps tendon (LHBT) with or without proximal amputation after arthroscopic rotator cuff repair in the treatment of repairable rotator cuff tear with LHBT injury. Methods The clinical data of 68 patients with LHBT injury combined with supraspinatus tendon tear who met the selection criteria between January 2016 and June 2020 were retrospectively analyzed. According to whether the proximal end of LHBT was cut off or not after arthroscopic rotator cuff repair, they were divided into LHBT fixation without cutting group (group A, 32 cases) and LHBT fixation with cutting group (group B, 36 cases). There was no significant difference in gender, age, operating side, preoperative supraspinatus tear width, Constant-Murley shoulder function scale, University of California Los Angeles (UCLA) score, and visual analogue scale (VAS) score between the two groups (P>0.05). The operation time, elbow flexion muscle strength, and postoperative complications were compared between the two groups. The Constant-Murley shoulder function scale, UCLA score, and VAS score were used to evaluate the recovery of shoulder function before operation and at 3, 6, 12 months after operation. The acromion-humeral distance (AHD) was measured by Y-view X-ray film of the shoulder joint immediately after operation and at last follow-up. AHD and acromion-greater tubercle distance (AGT) were measured by musculoskeletal ultrasound at 0°, 30°, 60°, and 90° of abduction. Results There was no significant difference in operation time between the two groups (t=–0.740, P=0.463). Patients in both groups were followed up (13.0±0.7) months in group A and (13.1±0.8) months in group B, with no significant difference (t=0.127, P=0.899). At last follow-up, the elbow flexor muscle strength of the two groups reached grade Ⅴ. Complications (including shoulder pain, deltoid atrophy, and rotator cuff re-tear) occurred in 6 patients (18.75%) in group A and 9 patients (25.00%) in group B, without neurovascular injury, surgical site infection, joint stiffness, LHBT spasmodic pain, and Popeye deformity. There was no significant difference in the incidence of complications between the two groups (χ2=0.385, P=0.535). The Constant-Murley shoulder function scale, UCLA score, and VAS score significantly improved in both groups at 3, 6, and 12 months after operation (P>0.05). The above scores in group B were significantly better than those in group A at 3 and 6 months after operation (P<0.05), and there was no significant difference between the two groups at 12 months after operation (P>0.05). Y-view X-ray film measurement of the shoulder joint showed that the AHD of the two groups at last follow-up was less than that at immediate after operation, but the difference was not significant (Z=−1.247, P=0.212); the AHD of group A was significantly greater than that of group B at last follow-up (t=−2.291, P=0.025). During musculoskeletal ultrasound detection of abduction and shoulder lift, there was no significant difference in the reduction degree of AHD and AGT in group A with abduction of 0°-30° compared with group B (P>0.05). The reduction degree of AHD and AGT in group A with abduction of 30°-60°, and the reduction degree of AGT in group A with abduction of 60°-90° were significantly smaller than those in group B (P<0.05). Conclusion In arthroscopic rotator cuff repair, whether the proximal structure of LHBT is cut off or not after LHBT fixation can effectively improve the symptoms of patients and promote the recovery of shoulder joint function. Compared with preserving the proximal structure of LHBT, cutting the proximal structure of LHBT after LHBT fixation has more obvious pain relief within 6 months, and the latter had better stability above the shoulder joint.