Abstract: The state parameter is the key of the unified constitutive model for clays and sands. Based on the state parameters, the MIT-S1 and CSUH unified constitutive models for clays and sands are compared and analyzed. Through comparison, the state parameter of the MIT-S1 model cannot be reasonably applied to the hardening parameters. It is difficult to accurately characterize the dilatancy of sand by using the LCC as the reference line to define the state parameter δp. Additionally, the state parameters are not unified. The CSUH model extends NCL of clays into that of sands, and the defined state parameter ξ can dynamically and unified represent different compactness states of clays and sands, accurately describe the basic properties of soils and act reasonably on the hardening parameter by M_c and M_Y. Therefore, the model is more concise and advantageous in describing the stress-strain relationship. By comparing the test data of clays and sands and the predicted results of the two unified models, it is further verified the accuracy of the CSUH model in describing the stress-strain relationship of clays and sands.