Abstract: Aiming at the unclear physical meaning of the parameters of small strain hypoplastic constitutive model for clay and the difficulty of engineering application, the constitutive model parameters were customized, and the subroutine of the small strain hypoplastic constitutive model for clay was developed. It was used to simulate and analyze the deformation process of Dortmund clay under monotonic load and Gaolin clay under cyclic load. Compared with the experimental results in the literature, the rationality of the subroutine was verified. Based on this, the developed subroutine was used to simulate and analyze the deformation characteristics of lacustrine sedimentary clay in Guanting Lake section of Beijing Zhangjiakou high speed railway under train dynamic cyclic load. The results show that with the increase of load cycles, the deformation of lacustrine sedimentary clay gradually increases and tends to be stable. The simulation results can better reflect the basic mechanical characteristics of cohesive soil under cyclic load, and are basically consistent with the test results, which verifies the applicability of the secondary development of small strain sub plastic clay constitutive model subroutine in practical engineering.