Interest in document content security (DCS) has grown rapidly in recent years. SRL integrates data application, security theory with related content, and it can solve many leakages in office automation. It has important applications in many fields such as education information system, enterprise resource management, Electronic government etc. First the research fields and different tasks of DCS are introduced and summarized. And then an introductory survey and overview of the DCS approaches is provided, and the approaches are classified into three families according to control mechanism. Each approach family is introduced. Finally, the current problems in DCS are discussed and future research directions are pointed out.