Background: With the extensive development of endoscopic sinus surgery, iatrogenic medial rectus muscle injury should be treated with caution. Traditional methods to repair a ruptured medial rectus need an anterior orbitotomy approach, with more injury and difficulty in finding the posterior end of the ruptured medial rectus. Objective: To explore a new method to repair a ruptured medial rectus. Methods: Eight cases of iatrogenic medial rectus rupture after endoscopic sinus surgery were reviewed from July 2015 to January 2019. Assisted by image-guided navigation, the ruptured medial rectus was sutured under an endoscopic endonasal orbital approach. Two methods were designed to suture the ruptured medial rectus. Optic nerve and orbital decompression were performed in 5 cases with visual impairment. The extent of exotropia and diplopia were followed up for 5 to 33 months after surgery. Results: With the help of image guidance, the posterior and anterior ends of the ruptured medial rectus of all patients were pinpointed, and operations using medial rectus anastomosis were successfully completed in 7 patients. The exotropia of these patients was corrected, and they have recovered. The vision of 2 patients recovered. There were no minor or major complications intraoperatively or postoperatively. Conclusion: Assisted by image-guided navigation, medial rectus anastomosis under an endoscopic endonasal orbital approach is a feasible method. The key to preventing orbital complications is strict professional training, including identification of the Onodi air cell and correct application of powered instrumentation.