Abstract： Objective To construct a three-dimensional finite element model of mandible and to analyze the stress distribution in mandible advaneed with Forsus.Methods One growing patient with mandibular retrusion was selected.After leveling and aligning with MBT(Mclanghlin BenneR Treriri)straight-wire appliance to achieve the request of forsus with the spiral CT,a three-dimensional finite element model was constructed and the stress distilbution in mandible after advancing at 1 second.15 seconds and 300 seconds wag analyzed.Results The three-dimensional finite element model included MBT stralght-wire appliance.The stress concentration areas were located in the front side of the condylar process.the sigmoid notch and mandibular molar areas at 15 seconds and 300 seconds after mandibular advancement.The maximum stress value8 were 34.47 MPa and 34.45 MPa.repectively.With the extension of loading time,the largest displacement increased from 3.30×10-2 mm to 1.15 mm and the regiOil of the largest displacement extended backwards along the bodv of mandible.However.the displacement of condyle reduced from 1.65×10-2mm at 1 second to 3.27×10-5 mm at 300 seconds after mandibular advancement.Conclusions The three-dimensional finite element model considered the viscoelasticity and viscoplasticity of mandibular.The result suggested that the stress distribution in the mandible gradually became stable after the application of Forfus and the appliance caused downward and forward mandibular modification.