Abstract: It is an important part of virtual orthodontic system that simulates and models the gingival soft tissue deformation.Aiming at the problem of"hyper-elasticity"of gingival exfoliated teeth caused by the traditional mass spring model when the external force was too large,the optimal threshold of the deformation spring was set by comparing the deformation effect and the deformation speed on the basis of the traditional"surface model".When the deformation spring was shortened or elongated beyond the threshold value,the spring length was restored to the original length as the initial length of the next single step deformation,so that the"surface model"has a"body"feature.The"sum of smoothness"was used to measure the smoothness of gingival surface after deformation,which gave a reasonable numerical definition of smoothness.The improved model and related models were implemented in VTK environment.The contrast simulation experiments of gingival soft tissue deformation were carried out on real scanned three-dimensional model data of jaw.The results show that the deformation speed of the improved model is increased by more than 28%and the sum of smoothness is obviously reduced.So,the improved model can solve the problem of hyper-elasticity well on the premise of higher deformation speed.