Compactness affects the long-term stability of port foundation engineering. To study the nonlinear creep characteristics of foundation soil under different dry densities conditions，the consolidation drained triaxial compression creep test of foundation soil is carried out. The results show that：1）With the decrease of dry density，the higher the moisture content of the soil after air pumping saturation，the greater the axial strain，and the more significant the creep behavior. 2）The long-term strength of soil increases with the increase of dry density，and the increase in dry density inhibits creep development. 3）The isochronal deviatoric stress-strain curve of foundation soil shows linear characteristics at low-stress levels and nonlinear characteristics at high-stress levels.Based on the experimental results of this paper，through the study of the relationship between viscoelastic modulus and dry density and loading time，the viscoelastic modulus considering different dry density is defined，and the fractional-order viscoplastic body is constructed based on the fractional calculus theory to obtain a new nonlinear creep mechanical model of soil under different dry density. The parameter solution method is given to verify the feasibility and rationality of the model. The empirical relationship between instantaneous modulus of elasticity and dry density is analyzed，and the recommended range of model parameters for similar silty clay foundation soil is given. The research results provide some reference for the study of creep characteristics of silty clay foundation soil and the long-term stability analysis of port foundation engineering.