Taking the marine soft soil of a port foundation in the Pearl River Delta as an example，we carry out the triaxial shear creep tests of consolidated drainage and consolidation undrained respectively. Based on the results of shear creep tests and the traditional Burgers model，we introduce a nonlinear SP element，obtain a new one-dimensional creep constitutive model after series connection，extend it to three-dimensional case，use the improved model to fit the shear creep curve of marine soft soil，and verify the rationality and correctness of the model. The results show that the marine soft soil shows instantaneous elastic deformation at each moment of loading，and then shows the stage of decay and stable creep，and the last stage of loading marine soft soil has accelerated creep. The axial strain and pore water pressure of each loading level are higher than these of drainage condition. The permeability of marine soft soil affects creep deformation，and the weak permeability condition is more conducive to the accumulation of creep deformation. The improved Burgers model is used to fit the shear creep curve of marine soft soil，which is in good agreement.