给出了信息安全的三层涵义，指出信息安全学科是自然科学与社会科学的融合体。从社会工程角度给出系统的概念，从部件、接缝、人员、环境四方面探讨了系统与信息安全的关系，提出了信息安全设计的必要步骤,并以通信系统为例分析了影响信息安全的因素。

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.