This study is devoted to the development of improved methods and computer programs for predicting the seismic performance of existing precast panel structures. It is necessary to establish an experimental investigation as well as to develop a more detailed analysis and design procedures related to seismic design considerations for existing precast panel structures. The nonlinear behavior of precast panel buildings depends on the panel contact zones and this feature should be incorporated into the analytical models for the elasto-plastic nonlinear analysis. This study presents a newly designed finite element program developed on Fortran software for the nonlinear analysis of typical precast panel buildings. With the aid of this finite element program, eight different analytical models were designed and performed to simulate the nonlinear behaviors of panel contact zones under lateral loading. The analytical models were composed of four control models without any retrofitting and four models retrofitted using a steel bolted plates at the both horizontal and vertical joints between associated panels. A two-dimensional elasto-plastic nonlinear analysis with pushover method was performed on the analytical models, to obtain lateral force and displacement relationship. The simulation results illustrate the comparisons of lateral force-displacement curves for both the non-retrofitted and the retrofitted models. It was observed that all the retrofitted models showed a significant increase in strength and ductility.