Purpose Superior capsular reconstruction (SCR) using fascia lata autograft has been performed for irreparable rotator cuf tear recently. The signal-to-noise quotient (SNQ) of the graft on magnetic resonance imaging (MRI) may relect the degree of graft maturity and healing. However, how SNQ changes with graft remodelling and time and whether this change correlates with postoperative clinical outcomes after SCR remain unknown. This study aimed to explore the correlation between SNQ of the fascia lata autograft and clinical functional outcomes after SCR. Methods Patients with irreparable posterosuperior rotator cuf tear undergoing SCR using fascia lata autograft between 2013 and 2017 were retrospectively analysed. For clinical outcomes, the American Shoulder and Elbow Surgeons (ASES) score, Constant-Murley score, Single Assessment Numeric Evaluation (SANE), and Visual Analogue Scale (VAS) for pain and range of motion (ROM; forward lexion and external rotation) were evaluated at postoperative 6 and 12 months. Signal intensity of the humeral, mid-substance, and glenoid sites and background were measured to calculate the SNQ values on follow-up MRI at 3 and 12 months. The correlations between clinical outcomes and SNQ at diferent time points were then analysed. Results A total of 15 patients were enrolled in the study. The mean postoperative VAS score signiicantly increased at postoperative 6 months and signiicantly decreased at postoperative 12 months. Except for forward lexion, all other functional outcomes were improved at postoperative 6 months. Analysis of MRI showed SNQ at the humeral (SNQh), mid-substance, and glenoid sites decreased from postoperative 3 to 12 months with a statistical signiicance detected in SNQh (P < 0.01). Correlation analyses showed that the SNQh values negatively correlated with VAS, ASES, Constant-Murley score, SANE, ROM (forward lexion), and ROM (external rotation) (all P < 0.05). Conclusion SNQ of the fascia lata autograft decreased with time in patients receiving SCR. SNQ at the humeral site was negatively correlated with clinical outcomes. Level of evidence III.