In general, a saturated frozen soil sample, as a composite material, consists of soil grains, ice and unfrozen water. The mechanical behavior of this kind of geomaterial is strongly affected by the amount of ice that fills the pore spaces. On the other hand, the amount of ice in a frozen soil sample depends on temperature and applied mechanical stresses. This coupled behavior is the main characteristic by which frozen soils behave differently compared to unfrozen samples. In this paper, by dividing the total stress into fluid pressure and solid phase stress, in addition to considering the cryogenic suction as an independent stress-state variable, an elastoplastic constitutive model for saturated frozen soils is proposed. When all water is unfrozen, the model will become a conventional critical state model. The coupling effect of ice content on the mechanical behavior, as well as the coupling effect in the reverse direction are taken into account in the proposed framework. The effect of temperature on the mechanical behavior is also considered in the model. The proposed model is able to represent many fundamental features of frozen soils such as frost heave and strength weakening due to pressure melting. The typical predictions of the model for simulating the characteristic trends of the frozen soil behavior is described qualitatively. Model predictions are also compared with the available test results and reasonable agreement is achieved.