Ecological risk assessment is a new study field that applies theories and methods of ecology, geography, environmental science and traditional risk assessment. Its objective is to estimate the possibility and magnitude that some undesired ecological events will occur by using mathematics, probability and other risk analysis techniques. These undesired ecological events are ecological endpoints brought by uncertain disasters or environmental accidents. In fact, ecological risk assessment is a method of drawing risk concept into ecological impact assessment. Regional ecological risk assessment is one branch of ecological risk assessment. It adapts to assess the possibility and magnitude of those undesired events affected on a regional scale. Compared with general ecological risk assessment, both the receptors and the sources of risk must be regional, the exposure and effects assessment must account their uncertainty and spatial heterogeneity. So, regional ecological risk assessment may be more complex. This paper inquires into the theory of regional ecological risk assessment and a set of assessment method. The main method steps of regional ecological risk assessment include regional definition and background analysis, risk receptor analysis, risk sources analysis, exposure and hazard analysis and integrated risk assessment. Then, regional risk management countermeasure can be put forward according to the assessment result.