The meanings in three layers on information safety are given.  It is proposed that all management,  strategy and technology are necessary to implement information safety,  because the science of information safety is the merger of natural and social sciences.  The concept of information system which includes elements,  boundary,  working condition and relevant people is proposed.  The relation between the system and information safety is analyzed,  and an example about information safety in communication is given.  The procedure of safety designing is suggested.