The work condition of the highway, which is usually built in mountainous regions, is complex relative to the ordinary road. Slope instability accident caused by the seepage of rainwater usually occurred in the rainy season. The mechanism for seepage failure of slope was investigated by used the Mohr-Coulomb criterion and the principle of effective stress. The effect of rain intensity on slope stability was equivalently instead by the effect of moisture content on slope stability. The influence of moisture content on the safety factor of slope stability was further calculated according to the Bishop’s method. The degeneration of safety factor follow to the moisture content was presented in the percentage.

Environmental conditions mountain road is more complex compared to other roads, subject to many affected, this explained the reason for the destruction of highway slope protection, and some reinforcement to optimize the design, and strive to economic rationality, the construction will be easy to put forward a theoretical basis for the construction of mountain highway.