This study investigates a unique type of soil, turfy soil, which is characterized by poor engineering geological properties and high organic matter content, widely distributed in the seasonally frost regions of Northeast China. The research discusses its freezing-thawing characteristics and the thermo-hydro-mechanical properties during the freezing-thawing process, which is of significance implications for parameter selection and frost heave settlement considerations in engineering construction within cold regions with high-organic-matter soil distribution. Unidirectional frost heave-thaw tests were conducted in the laboratory. Accurate hydrothermal characteristic parameters during freezing and thawing of a turfy soil were obtained by NMR and steady-state comparison method. Based on Fourier's law, the Richard equation, and considering latent heat of phase change and volume change during ice-water phase transition, a turfy soil-water-thermal-mechanical coupling model was proposed. Validation of this model using COMSOL Multiphysics showed that the errors between the frost heave and thaw subsidence of each soil layer and the measured values from tests were in the range of 1.75-3.6 mm and 0.75-1.73 mm, indicating a good fit. According to the simulation value, the turfy soil can be designated as strong freezing and thawing soil, matching reality. The results of this study provide a theoretical basis for the construction of roadbed and foundation project in the seasonally frozen turfy soil distribution areas and serve as a basis for frost damage prevention and control.