To analyze the fault of AC circuit that contained several energy storage components, a method based on phase analysis is presented. Firstly, the circuit program is developed by MATLAB software, Equation of output voltage of AC circuit is established in MATLAB. Secondly, the program of phase analysis is compiled in MATLAB language, this program convert sinusoidal signal to phase signal. Thirdly, circuit responses are obtained in different fault conditions through repeated modifying parameters of components. Finally, fault dictionary is constructed that these samples will be used to diagnose AC circuit in the future. A fault analysis example of AC circuit is provided. The result shows that this method has several advantages of simple algorithm, objective formulation, understandable signal, explicit figure, etc.