The flat plate system is an undefined seismic resistance system in the design code. In general, it is designed as a building frame system or dual system with shear wall, which has not yet been verified. In this study, we investigated the system level seismic capacity for 45 shear-reinforced flat plate systems using a nonlinear pushover analysis. Overstrength factor and a effective response modification factor are used to major parameters to define seismic capacity of the system, both of which are design factors of the seismic resistance system in the KBC2009 as an index. Analysis results showed that the effective response modification factor had exceeded the value presented in the KBC2009 in most cases. But, in some cases, the overstrength factor failed to meet the value presented in the KBC2009. Therefore, the flat plate system cannot be generally defined as a dual system with shear wall. But, plat plate system reinforced with shear band showed the efficiency of RC intermediate moment resistance frame except for 5-story case.