［］ Objective: To review the application and clinical effect of superficial temporal fascia fat flap in late-stage temporomandibular joint internal derangement. Methods: This study included 23 joints in 18 patients with late-stage internal derangement. All patients underwent TMJ discectomy and reconstruction simultaneously with pedicled superficial temporal fascial fat flap at the Department of Maxillofacial Surgery of the Affiliated Hospital of Stomatology of Nanjing Medical University from July 2022 to December 2023. Through regular follow-up,the preoperative and postoperative(more than 3 months) maximal interincisal opening, pain visual analogue scale(VAS),and self-assessment of joint function were compared. Radiological examinations were performed to evaluate the change in TMJ space. Results: The improvement of the mean preoperative mouth opening of (25.00±9.06mm)(11~40mm) to a mean postoperative mouth opening of (34.39±4.59mm)(25~42mm) was found to be statistically significant (P<0.001). The mean VAS pain score on 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=0.002). The mean scores on the self-assessment of joint function improved from (58.61±9.97) points preoperatively to (81.67±7.67) 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: Patients with late-stage temporomandibular joint internal derangement who underwent TMJ discectomy and immediate reconstruction with pedicled superficial temporal fascial fat flap could effectively improve mouth opening, relieve pain, and maintain the joint space.