With the rapid development of the expressway in the western mountainous areas of our country, it is inevitable to use elevated viaducts in the rock slope in order to satisfy the geometrical design requirements and to protect the environments. So that, it is definitely a key problem, that is to conform the rational design and safety in the projects and then provide the accuracy internal force analysis based on the fully understanding for its bearing mechanics, for engineers. In this dissertation those problems are detailed investigated and researched from theory and test fields in order to provide guidance for the practical projects, combined with the National Natural Science Fundation of china "study on the numerical simulation and design theory for rock slope bridge pile" (NO. 50578060) and the Transportation Technology Projects of Hunan Province "study on the design and protect technique for slope bridge pile"(No. 200513), and a series of design theories and computational methods are obtained for rock slope bridge piles.Firstly, the load transfer process of normal vertical bearing pile and passive pile under the vertical load、 lateral load and combinative load are discussed, and the primary differences between rock slope bridge pile and normal pile are listed. Based on that, a more sound load transfer model for the side resistance and tip resistance are established, which fully considered the multilayer characteristics of terranes around the piles and the change of side resistance by degrees. Then the calculation equation for settlement of the pile top in this model are developed, which makes it true that using the settlement of the pile top to control the vertical load capacity of pile. For the problem of rock slope bridge pile, after investigate its loading characters, its loads are disassembled into the vertical load on the pile top, lateral load, side glide thrusting force and the rock resistance around the pile. Based on the M- methods in design specification, the deflection differential equation of pile, using the slide plane are established. Employing the power series, the internal force calculate formula of pile are deduced which can be used to solve the internal force calculate problem for rock slope bridge pile.In order to fully understand the load characterize of rock slope bridge pile, the numerical manifold method is firstly be introduced into the pile engineering. Before the numerical solution are carried out, there are two key problems need to be conquest. One of them is the discontinuous deformation between pile and rock contact area, and