Fault modeling is crucial for power system simulation. There is no fast

accurate or complete method to model some common type faults（ such as N-1 fault

N-2 fault）

which troubles the system analysts. Firstly

two factors considering in fault modeling are analyzed

that is

fault route and fault action sequence

in which fault route is the difficulty of fault modeling.Secondly

a power system fault modeling method based on graph calculation is proposed with the consideration of the characteristics of power system data structure. Finally

a case of real power system is demonstrated to verify the availability of the proposed method. In future

the proposed method can be a theoretic foundation and practical tool for both on-line and off-line power system simulation.