Owing to a great variety of uncertainties，the actual power system usually faces certain vulnerabilities related to the inner and outer disturbances to make it go into abnormal operation states.Described in this paper are several possible typical precipitating factors making the power system go into abnormal operation states，including supernormal changes in the power grid structure，dramatic power fluctuation of intermittent energy，rapid ramping or dropping during peak or valley load periods.By analyzing the typical scenes of abnormal operation states and tendencies of power networks，the causality between scenario and state and the difference between state and tendency are sorted out for power systems.On this basis，state features and tendency indices are set up to embody the abnormal operations of power systems，and the corresponding assessment framework and methods are also given.Furthermore，guiding principles for parameter setting are given，and feasible comprehensive evaluation methods for abnormal operation states and tendencies are analyzed.