Mobile robots in unknown environment have little a-prior information. Therefore,environmental cognition is the basis of the environment modeling,self-localization,planning and action for autonomous navigation. The research on environmental cognition theory and methodology relates to computer science,artificial intelligence,psychology,neuroscience,bionics,and so on. It is an important frontier research field of the interdiscipline subject of cognition science. The current status of theories and methods for environmental cognition of mobile robots under unknown environments are surveyed and analyzed. Existing problems are presented and issues of future research are also proposed.