In this paper, 27 cases of mandibular fracture with displaced fragment were divided into experiment group fixed by plate following AO principles and control group fixed by IMF. Through postoperative evaluation separately at the first, second, third month by means of X-ray, occlusal analysis based on dental models before and after fracture, occlusal force recording in areas of molar, premolar, incisors, and investigation of mandibular movement function during mastication, the results show that: (1) Occlusal relationship is not as satisfied as considered previously when IMF is used to treat mandibular fracture. In some cases, the dental cusps of molar and premolar don't contact tightly in lingual side, the occlusal plane seem to be inclined bucco-lingually. (2) The use of DC plate or EDC plate can avoid long-time IMF and reduce its complications, allow early function of mandibular fracture and follow the principles of biomechanics of combining mobility with static. As long as exact operative procedures, better occlusion than the use of IMF can be achieved.