On the basis of the internal force and deformation formulas of straight and curved elastic foundation beams，a program is organized and applied to structure stress analysis of the reinforced concrete bifurcation pipes of the underground penstocks in Panshitou Reservoir. The computational section of the bifurcation pipe is simplified to a combination structure of uniform ?straight beams and circular curved beams.The internal forces at key points under four kinds of working conditions are calculated, the results provide foundation for the reinforcement design of the bifurcation pipes.