Abstract: The hypoelastic constitutive model of periodontal ligament was built and investigated. The validation of using hypoelastic model to describe the mechanical character of periodontal ligament was analyzed, a hypoelastic model of periodontal ligament based on uniaxial extension data was deduced and built, with a hypothesis of isotropy and small strain. A viscoelastic model based on hypoelastic model and its parameter was derived. A dental finite element model was built to conduct analysis, with the same boundary condition of experiment in literature. The analysis result conforms to the experimental result. It is concluded that the character of periodontal ligament can be represented well with an isotropic hyperelastic model，the constitutive model of periodontal ligament is only an equivalent model and should be built according to the boundary condition adopted in finite element analysis.