Ecological security is an important support and component of national security, with the implication of the avoidance of ecological degradation issues, and the effective support to economic-social development and human well-being from ecosystem services. For a long time, however, the understandings of the concept and connotation of ecological security have varied with researchers and decision-makers, and the focuses and approaches of ecological security assessment also have not been unified with multifarious limitations, which were obviously not conducive to the related researches and practices. Thus, based on the review of ecological security concept and connotation with the progress, this paper highlighted the content of the systemic characteristics of ecosystem and its close relation with human well-being. It makes clear that ecological security has two meanings, according to the aspects of the material basis of ecosystem, and its contributions to the development of human society. We summarized the current case studies on ecological security assessment. In these researches, the indicators based on the pressure-state-response 3-dimension system, or a similar one including dimensions like climate, ecology and environment, society and economy, etc., were commonly used with the synthesizing method of weighted addition. Such approaches directly synthesizing the basic elements of ecosystem and society with different properties and dimensions, have not only hindered to highlight the key systemic characteristics related to ecological security, but also deviated from the actual meanings of those different dimensions, without the reflection of the dynamic of ecological security. Therefore, this paper elaborates the strategies of the ecological security assessment approaches by focusing on ecological degradation issues and ecosystem services, which can reflect the core connotation of ecological security, building the indicator system with the characteristics of relativity and dynamics, and selecting the proper indicator-synthesizing method, based on the related research progress. Finally, as to the assessing approaches of the ecological security, we put forward some specific prospects for further research, including the appropriate formulation and improvement of indicator system and synthesizing method for ecological security assessment, the thorough exploration of the relationships between ecosystem service and economic-social development with the meanings of ecological security on human welfare, the prior concern on the ecological security and its assessment of the typical eco-fragile area, and the scientific prediction for ecological security under climate change scenarios in the future. These works are expected to provide some insights for the research and practice of regional ecological security assessment, ecological civilization construction and national security.