Abstract: Deep beam is one of the structural members used frequently in engineering, such as the walls of bunker,etc, Because the stresses in deep beams are complicate,in the past,they were solved by using triangular series, finite-differencemethod, or the recent finite-element method.But the mechanical mechanismof deep beams can not be clearly identified from these numerical approaches.In this paper, the solution based on the mechanics of bar system is given .It is not only easy to get a global picture of the stress, but also convenientto be used by engineers.