The invention discloses a method and a system for identifying large cascading failure events of a power grid, and belongs to the technical field of power system safety. The method comprises the following steps: 1.1, obtaining a power grid operation state by utilizing a power grid real-time state tracking technology; 1.2, screening the anticipated event set according to a preset index; 1.3 selecting risk elements in the anticipated fault set, exiting the operation of the risk elements, and verifying the risk elements; 1.4, performing power flow calculation on the whole grid to obtain a calculation result, if the calculation result is not convergent, cutting off the risk element, and listing the cut-off risk element fault as a to-be-evaluated large event; 1.5, when it is determined that thepower grid has no overload or three overload lines are disconnected, obtaining a consequence index of an anticipated event, and when it is determined that the power grid has overload and the three overload lines are not disconnected, disconnecting an overload element as a lower-level event, and entering 1.4; and determining the large event according to the large event evaluation index. According to the method, the large event of the cascading failure of the power grid can be pre-identified, and corresponding prevention and control measures are taken according to the identification result.