Abstract: Objective To develop a new threshold segmentation method for mandible image segmentation. Methods CT data of 12 volunteers were exported into Mimics 10.01.An improved method usinga narrowed threshold range (the maximum threshold range that can segment mandible without manual efforts) was developed in 3D reconstruction, and compared with the traditional method. We used dilation operations to make up the information loss of image borders, by which we obtained an approximate segment result. A precise segment resultwas eventually arrived with the help of logical operations and region growing. We compared mean time consumptions of the two methods, as well as their 3D reconstruction results using Geomagic Studio 11.0. Results The new method generated a success rate of 91.67% (11/12), with a mean time consumption of (319.7±125.3) s. The traditional method took much longer time 〔(1 261.3±427.3) s， P<0.05〕 than the new method. Compared with the reconstruction results of traditional method, the new method had an outward deviation of (0.066±0.011) mm and an inward deviation of (0.070±0.008) mm. Such deviations were less than the minimum distance that a naked eye can discern.The lower limit of the widest threshold range which mandible could be isolated was (507.72±100.31) HU, while the upper limit was (1 133.33±47.57) HU. Conclusion The new method we proposed can improve the efficiency of threshold segmentation of mandible.