Abstract:A soft-matter element and its constitutive equations were presented by employing the Riemann- Liouville fractional calculus operator theory. The element could be used to simulate the soil of which behaviors were deemed as the materials between perfect solid and fluid;it also could be used to describe the nonlinear slow-variable process of stress-strain in stress relaxation or creep. Two new models were determined when a soft-matter element was parallel to or series connected with an elastic element. The constitutive equations,relaxation modulus and creep modulus could also be obtained. A rheological trial fitting curve of soil was provided. The achieved results show that the proposed model with soft-matter element was more efficient in describing the rheological characteristics of soil and could reduce the number of parameters.