The traditional loess constitutive model is mainly composed of elastic model and elastic-plastic model. However,the assumption of elastic model on soil is too simple,and the elastic-plastic model sometimes does not meet the law of thermodynamics. Therefore,the loess constitutive model for elastic-plastic deformation based on the principle of maximum energy dissipation rate is more rigorous. Based on the constitutive model,a laboratory test scheme was designed to obtain the parameters of the model. Taking Southern Jing-Yang plateau as the study area,the value range of constitutive parameters and the form of hardening function of Q₃ Malan loess under different water content were studied. The results show that:the hardening function of the plastic shear strain of Q₃ Malan loess in Southern Jing-Yang plateau is hyperbolic,the value of parameter a ranges from 0.002 to 0.02,and that of parameter b ranges from 0.01 to 0.05; the hardening function of the plastic body strain is cubic,and its parameters m₁、m₂、m₃ are between 0.001 and 1;the volume modulus K ranges from 40 MPa to130 MPa and the shear modulus G ranges from 20 MPa to 60 MPa; compared with the experimental data,the constitutive model can accurately describe the stress-strain relationship of Q₃ Malan loess in Southern Jing-Yang plateau by using the parameters obtained from the experimental scheme.