Abstract: The deep overburden layer has significant in-situ structural effects, and how to determine the constitutive model parameters by considering the in-situ structure effects is related to the reliability of safety assessment results. The in situ pressuremeter tests are carried out on the silty clay in deep overburden layer, and the load-displacement curves are measured, and the characteristic values of mechanical indexes such as bearing capacity characteristic value and pressuremeter modulus at corresponding depths are determined. Combined with the results of the in-situ pressuremeter tests and laboratory triaxial test, the constitutive model parameters of silty clay in deep overburden are determined by using the PBP3 back analysis program based on the harmony algorithm. The process of the pressuremeter tests is simulated by using the back analysis parameters and laboratory test parameters respectively, and the rationality of the back analysis parameters is demonstrated by comparing with the measured load-displacement curves.