In a method of critical displacement forecast based on the deformation failure mechanism of slope, a sliding surface displacement, a calculation based on status stability factors and a slope surface displacement are determined, and applied for forecast based on a thrust-type slope deformation mechanism, a key compartment division, a relation between stress and strain mechanics properties of sliding surface of geo-material, and an analysis of evolution characteristics at different points of the sliding surface. The method provides advantages of determining deformation values at different points of a sliding surface, a slope body and a slope surface during slope failures; describing the process of a progressive failure, deformations and force changes of a slope; combining slope monitoring values to perform the stability analysis and the calculation of the magnitude of the stability factors in different deformation statuses of the slope; and assessing the durability of protective measures to the slope.
