Space division multiplexing,as a possible solution to overcome the limitations of single-mode fiber communication system,has attracted more and more attentions in recent years. It has a variety of implementations,such as multicore fiber,MIMO processing,mode-division based on multimode fiber and space optical component. Some solutions of mode multiplexing are analyzed,their principles are elaborated,and the latest progress of each solution is introduced. Finally,the characteristics of the various solutions have been reviewed.