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The theoretical research on soft-terrain machine systems has scientific significance and engineering application value to agriculture, forestry, mining and military. Firstly, the development on research of the basic theories and the latest research on soil—wheel interaction relationship of soft-terrain machine systems were reviewed. Then, the anti-adhesion and resistance reduction mechanism of soil animal from morphology, structure and flexibility, as well as the bionic theoretical basis for terrain-machine soil-engaging component were also reviewed. Secondly, the measurement methods for terrain mechanical properties and the soil bin testing equipments for the research were introduced. Moreover, the development on research of numerical simulation methods for the terrain machine systems was analyzed and summarized. Finally, the applications of the terrain machine systems theories and methods for soil-engaging component and vehicle motion mechanism in the future were discussed.