Based on MRI results, pre- and post of arthroscopic rotator cuff repair to evaluate the correlation of fatty degeneration index (GFDI) in the healing tendon group (Sugaya's index) and the re-tear group of the post-operative rotator cuff repairs. Descriptive prospective study of 114 Vietnamese patients with rotator cuff tears, who had repaired RC by arthroscopic shoulder in Military Hospital 175, from May 2015 to November 2017. Evaluation of the GFDI classification on MRI and clinical exam before operation 82 patients had postoperative MRI. Healing tendon patients (I, II, III grade) that made up the majority of patients taking MRI post-operative were 73 patients (89,02%). Re-tear tendon patients (IV, V grade) were only 9 patients (10.98%). GFDI index was usually I and II grade preoperative (50% grade I and 25.6% grade II) and postoperative (50% and 29.3% grade II). Average GFDI before and after surgery had not significant difference. Retear postoperative group’s average GFDI index is significantly higher than that of the healing tendon group both before surgery (3.00 ± 0.707 compared with 1.34 ± 0.803) and after surgery (3.00 ± 0.500 comparison with 1.29 ± 0.716). This result had statistical significance. All retear patients’ GFDI indexes were IV and V. GFDI indexes and average GFDI index between pre- and post-operative in RCT had no significant difference. GFDI in the re-tear group (IV, V based on Sugaya's) was dramatically higher than that in healing tendon group before and after surgery.