Mega steel braced frame-composite steel plate shear wall structure, consisting of mega steel braced frame as outer frame and composite steel plate shear walls as core wall, is a new type of hybrid structure that is proposed in this study. Seismic performance of this new structure was analyzed under frequent earthquake and severe earthquake. The analysis focused mainly on displacement response, seismic base shear distribution and failure mechanism. Comparing with traditional steel frame-RC core wall structure, this new type of hybrid structure presents better coorporative working performance since mega steel braced frame provides larger stiffness and composite steel plate shear wall provides a fairly ductile response. It can be observed from the failure mechanism that this structure has multiple seismic resistant systems with composite steel plate shear wall, mega braces and mega frame when subjected to severe earthquakes.