“Vulnerability”is a new research frontier in the domain of sustainability science and global environment change, and the term is now a central concept in a variety of research contexts such as natural hazards, climate change, land use change, and sustainable development; meanwhile, vulnerability research is perceived by many researchers as a new science which deals with the mechanism, the process of interactions between human and environment, and the regional sustainable development. Finding a generally applicable conceptual framework and robust assessment methods of vulnerability which are key factors to determine the development of vulnerability science, is a challenge facing vulnerability science. Recent years, researchers from different disciplines draw growing attention to the concept and assessment methods of vulnerability, leading to a rapid progress on the concept and assessment methods of vulnerability. The paper analyzed the different definitions of vulnerability from literatures both abroad and domestic, and illustrated the convergences and divergences among these definitions; based on this, we discussed the exact meaning of the term, maintaining that the sensitivity and coping capacity of system to perturbations impinging on it are the main characteristics of vulnerability of system. In addition, we reviewed the methods used in vulnerability assessment, and classified these methods into five categories according to their assessing process. we evaluated the weaknesses and strengths of each method respectively, then put forward some principles that should be followed in the process of vulnerability assessment, such as choosing simple assessment methods at first and then, with complicated ones later, paying attention to the trade- off between data transformation and results interpretation, focusing on key processes of the generation of vulnerability and making use of multiple methods in a complementary manner. Finally, according to the new trends in vulnerability research, the paper brought forward some issues which should receive more attention in the vulnerability assessment research, such as the vulnerability to multiple perturbations, the vulnerability of coupled systems, the uncertainties of complex system, and the scale issue in vulnerability assessment.