The invention discloses a real-time diagnostic method and system for the operating state of a power grid. The real-time diagnostic method includes the steps of acquiring operating state information of a power grid device and transmitting to an electric power dispatch center; storing, in the electric power dispatch center, power grid parameter information which does not change with the operating state of the power grid; and conducting, by the electric power dispatch center, power grid operation diagnostic analysis and outputting the analysis result according to the received operating state information of the power grid device and the power grid parameter information which does not change with the operating state of the power grid, wherein, the diagnostic analysis includes flow security check of the real-time operating state of the power grid, short-circuit security check of the real-time operating state of the power grid, stability security check of the real-time operating state of the power grid and the real-time economic efficiency check of the real-time operating state of the power grid. The invention can monitoring the operating state of the power grid in real time, quickly determine the operating security problem and economic efficiency of the power grid and give quantitative evaluation indicators; can well meet the needs of different operating modes of the power grid; and provides a reference for power grid dispatching and operation.