In the past researches, the influence of the weigh for the masonry infill walls on reinforced concrete frame was only considered in the calculation of the structure for the reinforced concrete frame buildings with masonry infill walls, the action of lateral resistant thrust of the masonry infill walls to reinforced concrete frame was usually neglected. A large of model experiments, theoretical analyses and investigations for the damage due to earthquake have been shown that reinforced concrete frame buildings with the masonry infill walls can not only raise the lateral resistant thrust of whole structure, but also put off the production of plastic hinge and raise the bearing capacity of whole structure. In this paper, a mixed element model was made up of the element for reinforced concrete frame bar and the plane element for masonry infill wall, This model, which was loaded by the statically admissible in groups horizontal load P and the identical vertical load was analyzed. The bending moments M, on the column ends was obtained. The limited bending moments M(o) was calculated under the given stiffness, reinforcement bar and ratio of axial pressure. From the calculation and comparison, the distinguish conditions of plastic failure under various the masonry infill walls and different stiffness were obtained, the mechanism of the plastic hinges on the frame was discussed.