Abstract: The main difference of stability evaluation between the mountainous highway exhibition subgrade and the ordinary subgrade lies in the interacting distortion of various highway subgrades. Namely the partial subgrade deformation initiates the deformations of nearby subgrade and even the entire subgrade around a mountainous section. Meanwhile the interaction matrix especially qualifies to solve complex questions concernign interactions and mutual coupling of various factors. The interaction matrix is introduced to establish a stability evaluation method which is possible to consider the basic parameters of highway exhibition subgrade and the mutual influence among variables, that is the coordinated method of highway exhibition. This method is used to evaluate the stability of a highway exhibition subgrade and slope system that contains two roads. In the overall evaluation all informations about engineering design, construction and operation of this system are considered. The method considers influences of each parameter on the overall system and the contribution of parametric interaction to the overall system.