A seismic performance evaluation methodology developed as part of the SAC Joint Venture has been applied to various building systems. Among them, RC shear wall buildings as a lateral load resisting system with flat plate system as a gravity load resisting system have been evaluated using the methodology. Since the performance evaluation was executed based on approximation of various parameters, however, the results can be variable if different approximation is applied. Therefore, it needs to understand the factors to affect the performance of RC shear wall buildings with flat plate and to investigate the sensitivity of the factors to the performance. In this study, the factors were story drift limit of shear wall, deformation mode of flat plate column, and shear reinforcing of flat plate slab. The results showed that the performance was highly affected by change of the factors. Specially, besides RC shear wall itself, the behavior of flat plate column and slab is very significant because they behaves simultaneously with RC shear wall.