Non-linear stiffness at small strains is one of important intrinsic soil features and is vital to finite element analysis of deep excavations. This paper introduces determination of HS-Small model parameters for typical Shanghai clay layers (② ~ ⑥)through a series of laboratory tests. A method by which stiffness parameters E_oed^ref, E₅₀^ref, E_ur^ref and small strain shear modulus G₀^ref can be deduced from compression modulus E_s1-2 has been proposed. The values of parameters R_f,m,v_ur,γ_0.7 are also suggested. Together with shear strength parameters of c′、φ′ provided in geotechnical investigation report, the HS-Small model parameters are determined. Finally, Based on the small strain model parameters determined by this method, the three-dimensional numerical analysis of Yunlingxi ultra-deep shaft structure of Shanghai deep tunnel drainage system is carried out, and the applicability of small strain constitutive model in ultra-deep foundation pit engineering is verified.