The invention discloses an electric system fault diagnosis method. The method is characterized in that, to begin with, a voltage analog signal and a current analog signal of an electric power line is detected through a voltage transformer and a current transformer respectively, and the current analog signal and the voltage analog signal are converted into a current digital signal and the voltage analog signal, which are then, input to a grid fault analysis device; a current detection unit and a voltage detection unit of the grid fault analysis device carry out comparison and analysis on the detected signals and stored standard signals through a comparison and analysis unit, then, enable fault signals obtained after comparison to be stored in a storage unit and enable the signals to be sent through a sending unit; the grid fault analysis device enables the input current digital signal and the voltage analog signal to be subjected to comparison and analysis with the standard signals stored in the system to determine the fault signals; a receiving unit of a server receives the fault signals and fault location is carried out through a line fault location unit to determine causes of the fault; and the server receives the fault signals to locate a fault point, and fault diagnosis is carried out through a fault diagnosis module.