Abstract: The state parameter is the key of the unified constitutive model of clays and sands. Based on state parameters, MIT-S1 and CSUH unified constitutive models of clays and sands are compared and analyzed in this paper. 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 LCC as the reference line to define the state parameter δp. Additionally, the state parameters are not unified. The CSUH model extends clay NCL into sand, and the defined state parameter ξ can dynamically and unified represent different compactness states of clays and sands, accurately describe the basic properties of soil and act reasonably on the hardening parameter by Mc and MY. Therefore, the model is more concise and advantageous in describing the stress-strain relationship. By comparing the clays and sands test data and the prediction results of the two unified models, it is further verified that the accuracy of the CSUH model in describing the stress-strain relationship of clays and sands.