Abstract: To study the mechanical properties of frozen peat soil in the deep sedimentary facies of Dianchi Lake, the experimental method of "long-term high-pressure K0 consolidation - loaded freezing - loading" was adopted. The effects of freezing temperature, confining pressure and moisture content on the mechanical properties of frozen peat soil were explored through indoor low-temperature triaxial experiments, and the theory of binary medium constitutive model was introduced to analyze the deviatoric stress-strain relationship. The results show that the pressure coefficient K0 value of peat soil is 0.5. The deviatoric stress-strain curve of frozen peat soil can be divided into the linear elastic growth stage, the elastoplastic deformation stage and the stable stage. The peak strength is positively correlated with the confining pressure and moisture content, and negatively correlated with the temperature. The cohesive force and the internal friction Angle fluctuated within the ranges of 418.72-571.96kPa and 14.53°-17.72° respectively. With the decrease of temperature, the cohesive force increased and the internal friction Angle decreased. Based on the experimental results, a binary medium constitutive model suitable for deep frozen peat soil was constructed, verifying its rationality and demonstrating high applicability and accuracy.