Based on the structural modified Cambridge model, a critical state constitutive model for natural loess is established by considering the structural evolution and initial anisotropy of natural loess. The anisotropy characteristics of natural loess are reflected by introducing anisotropy parameters in yield surface in this paper, hardening criterion and critical state description based on the quasi-modified Cam-clay model which can reflect soil structure. Furthermore, the critical state elastoplastic constitutive model of saturated natural loess is derived by using the non-correlated flow rule. The model established in this paper has nine parameters. Compared with the traditional modified Cam-clay model, three parameters reflecting the structure and one anisotropic parameter are added, which can be determined by conventional triaxial test. The results show that the constitutive model can better describe the structural and anisotropic characteristics of saturated natural loess.