In this paper, earthquake-resistance behaviors of existing masonry structures are evaluated based on a certain masonry building. The existing masonry structure is evaluated in its defects of primary design and construction measurements, seismic bearing capacity and durability. Based on results of evaluation, the seismic reinforcement design is introduced for improving earthquake-resistance behaviors of the whole building and its weak positions. In the seismic reinforcement concept design, the ductility of the masonry structure is improved in bearing seismic loading and plastic deformation. Further more, the masonry building is reinforced for avoiding collapse due to the weak positions of its bottom and top layers, stair halls, short walls and wall corners. Evaluation results and the corresponding seismic reinforcement design are significant for safety of both existing and newly designed masonry structures in earth-quake areas.