Based on the asymmetric characteristic of skeleton curve obtained from dynamic tests on soils,a function with double asymptotes is proposed for describing the dynamic constitutive relations of soils.The hysteresis loops observed during unloading and reloading show the same form as the skeleton curve and are constructed by taking the ultimate stress as the corresponding asymptote.The coeffcient of initial unloading modulus is used to ensure that the constructed hysteresis loop fts well with the experimental data.Then,a new dynamic constitutive model considering the asymmetry of skeleton curve is elaborated.The verifcation tests on saturated Nanjing fne sand are performed using a hollow cylinder apparatus to verify the applicability of the UD model.It is found that the predicted curves by the UD model agree well with the test data. Based on the asymmetric characteristic of skeleton curve obtained from dynamic tests on soils, a function with double asymptotes is called for describing the dynamic constitutive relations of soils. Hysteresis loops observed during unloading and reloading show the same form as the skeleton curves and are constructed by taking the ultimate stress as the corresponding asymptote. The coeffcient of initial unloading modulus is used to ensure that the constructed hysteresis loop fts well with the experimental data. Chen, a new dynamic constitutive model considering the asymmetry of skeleton curve is elaborated.The verifcation tests on saturated Nanjing fne sand are performed using a hollow cylinder apparatus to verify the applicability of the UD model. It is found that the predicted curves by the UD model agree well with the test data.