The invention discloses an identification method of a complex power grid self-organization critical state in the technical field of electric power system cascading failure prevention. The method includes: obtaining actual load loss caused by random failures occurring on a power grid; calculating cumulative probability of the random failures occurring on the power grid according to the actual load loss caused by the random failures occurring on the power grid and set load loss amount; performing regression analysis on the set load loss amount and the cumulative probability so as to determine whether the power grid is in a self-organization critical state; calculating a power grid load loss expectancy value and determining relative probability of load loss failures occurring on the power grid when the power grid is in the self-organization critical state. The identification method enables users to accurately judge whether the power grid is in the self-organization critical state at present, obtain probability of cascading failures occurring on the power grid, calculate load loss amount after the cascading failures occur and meanwhile estimate relative probability of large-scale power failures caused by the load loss.