Design an extended osteotomy guide (EOG) for Le Fort I osteotomy to improve the safety of surgery.The digital Le Fort I osteotomy guide was designed in MIMICS 23.0. Twenty-eight patients were randomized into 2 groups. Patients in the experimental group used EOG, and patients in the control group used a traditional osteotomy guide (TOG). Virtual designs and actual postoperative outcomes were compared by cone-beam computed tomography. The safety of the operation was confirmed by the accuracy of the osteotomy direction and depth on the inner and posterior walls of the maxilla.All positioning deviations of both osteotomy guides were0.3 mm (P0.05). The osteotomy depths on the inner and posterior walls with the EOG and TOG deviated by 0.789±1.179 and 1.811±1.345 mm (P=0.004) and 0.648±0.999 and 1.262±0.942 mm (P=0.030), respectively. The angles of deviation of the osteotomy direction on the inner and posterior walls by the EOG and TOG were 2.025±2.434 and 5.069±2.391 degrees (P0.001) and 2.772±2.979 and 8.653±4.690 degrees (P0.001), respectively.The EOG was more accurate than TOG for manipulating osteotomy direction and depth on the inner and posterior maxillary walls. Thus, EOG could ensure higher surgical safety than TOG.