Online assessment of power system cascading failure lies in acquiring physical models and real-time data. A method based on CIM/E for power system cascading failure online assessment is proposed. In view of power system physical models and data characteristics, on the basis of applying CIM/E to power system cascading failure online assessment, document check、data extraction and data processing of CIM/E and island recognition are researched. Then a complete cascading failure online assessment scheme of regional system is presented combining the above method and credibility measure. Through system development and application in China"s southwest practical regional system, both the correctness and the effectiveness of the proposed application were verified, and the method is able to timely and accurately provide decision-making basis for the dispatching personnel.