Abstract: The instantaneous settlement of high railway foundation in loess area is closely related to the mechanical properties of saturated compacted loess. The constitutive relationship of saturated compacted loess is an important means to characterize its mechanical properties. Because Duncan-Chang constitutive model is difficult to accurately describe the strain softening characteristics of compacted loess after failure, in order to improve the adaptability of Duncan-Chang constitutive model, statistical damage theory is introduced to establish Duncan-Chang damage constitutive model of saturated compacted loess. Q_3 loess in Xiyan high-speed railway filling area was selected, consolidation undrained triaxial tests with different compaction degrees were carried out, the vumat subroutine was written for verification, the triaxial test of saturated compacted loess and the finite element numerical simulation analysis of subgrade settlement under different compaction degrees and filling slopes were realized. The results show that the compacted loess in the filling area shows strain softening characteristics when it is sheared. The peak strength and initial deformation modulus increase with the increase of compaction degree, but the increase of peak strength decreases with the increase of compaction degree, while the increase of initial deformation modulus increases with the increase of compaction degree; The vumat subroutine based on Duncan Chang constitutive model with statistical damage is used to verify the shear strength of compacted loess in triaxial test, and the results are basically consistent, which can better reflect the mechanical characteristics of strain softening of compacted loess in filling area; Through vumat calculation, the settlement of filled subgrade decreases with the increase of compactness, and increases with the increase of fill slope. The research results can provide reference for the calculation and analysis of the instantaneous settlement of fill subgrade in loess area.