In this paper the author applied mechanochemical self-catalysis phenomenon resaerch results in solid mechanochemistry to analyse quantitatively the mechanism of forming land slide split-plane. With the aid of the method joining the irreversible process thermodynamic theory into reaction practice of kinetics, the paper studied the slope mechanochemical process from descending rock strengh, forming and spreading joint, and linking up split planes together, to lose balance under the coordinated effect of weight stress and active water. The paper probed into a new applied question that applied solid mechanochemical theory to landslide research.