<p>A precise assessment of the mechanical characteristics of the slip zone is essential to implement the stability analysis of landslides. This article examines the mechanical properties of slip zone soil using large-scale direct shear tests and ring shear tests while taking into account the over consolidation ratio (OCR) and particle grading factors. The mechanism of soil particle behavior was examined from a macro-meso perspective to account for the mechanical characteristics observed from the tests. Further, the three determined groups of mechanical characteristics were employed in the landslide numerical model, respectively. The comparability between the simulative results and field monitoring data was examined, and then the suitability of the strength parameters to the landslide was explored. Results indicate that the landslide deformation and its mechanism can only be accurately described when the OCR of samples and the original particle gradation are considered. In this way, a superior technique for determining the soil in the slip zone is established, which has great significance for landslide modeling.</p>