Abstract: In order to establish the constitutive model that can simultaneously reflect the unsaturated state, transverse isotropy and nonlinearity of soils, the mechanical properties and constitutive models of unsaturated transverse isotropic soils are systematically studied. First, an incremental nonlinear transverse isotropic constitutive model for unsaturated soils is established based on the theories of unsaturated soil mechanics and elasticoplasticity. Next, the triaxial tests on unsaturated soils with various stress paths are carried out, revealing the deformation strength characteristics and water volume variation characteristics of unsaturated transverse isotropic soils. Again, the variation laws of model parameters with stress state are analyzed, and the corresponding mathematical expressions are put forward. Finally, the variation laws of model parameters with stress state are analyzed, and the corresponding mathematical expressions are put forward. The research results can provide scientific basis and theoretical support for the design of natural layered foundations and large-area filling projects. The research enriches and develops the constitutive model theories of unsaturated soils.