Objective：To explore the application of superficial temporal fascia fat flap in late-stage temporomandibular joint internal derangement（TMJID）. Methods：A retrospective analysis was conducted on 18 patients（21 joints）with late-stage TMJID who visited the Department of Maxillofacial Surgery of the Affiliated Hospital of Stomatology of Nanjing Medical University from July 2022 to December 2023. All patients underwent TMJ discectomy and reconstruction simultaneously with pedicled superficial temporal fascial fat flap. Preoperative and postoperative evaluations（more than 3 months）included maximal interincisal opening，pain visual analogue scale（VAS）scores，and self-assessment of joint function. Radiological examinations were performed to evaluate the change in TMJ space. Results：Among the 18 patients，17 were female and 1 was male，with an average age of（42.22±16.90）years. There were 12 perforated articular disc，accounting for 57.14% . The improvement of the mean preoperative mouth opening of（24.00±7.94）mm to a mean postoperative mouth opening of（34.83±4.48）mm was found to be statistically significant（P < 0.001）. The mean VAS pain score on maximum mouth opening decreased significantly from 50（25，75）points to 0（0，25）points（P < 0.001），while the VAS pain scores on diet reduced from 50（0，75）points to 0（0，0）points（P=0.001）. The mean scores on the self-assessment of joint function improved from（58.06±7.50）points preoperatively to（81.67±7.28）points postoperatively and were found to be statistically significant （P < 0.001）. Compared with the preoperation，postoperative radiological examinations showed that the anterior，superior and posterior joint space were significantly increased after surgery（P < 0.05）. Conclusion：Replacement of the perforated joint disc with a superficial temporal fascia fat flap can improve mouth opening，relieve pain，and maintain the joint space stability. This technique is an effective treatment for late-stage TMJID.