AIM: To develop a feasible method to correct congenital ptosis in children. METHODS: Sixty-four patients (102 eyelids) were divided into three groups based on the degree of ptosis: mild (<2 mm); moderate (3-4 mm); and severe (>4 mm). All patients underwent the same levator resection surgery in which the suspensory system of the LPS is retained. After capturing a standard photograph of primary position, the height of the superior palpebral margin was measured preoperatively by using Image J software to calculate its ideal height required during surgery. Postoperative outcome measures included upper eyelid margin height, degree of scleral exposure and exposure keratitis. The patients were followed-up at 1wk, 1mo and 6mo postoperatively. RESULTS: In the early postoperative period, except two cases with overcorrection, the positions of the eyelid upper margins were normal in all cases in the mild and moderate groups. Six months postoperatively, the eye with overcorrection in the moderate group showed improvement, while the eye in the mild group did not. Seven eyes in the severe group exhibited residual ptosis to varying degrees. The eyelids exhibited appropriate closing functionality; exposure keratitis was absent. CONCLUSION: Using this preoperative quantification technique to guide surgery not only provide a gauge for LPS shortening under general anesthesia, but also increase the success rate of surgery.