The invention discloses a high-risk cascading failure accident chain search method for a power system. An existing complex network theory-based accident chain model ignores particular characteristics, including an electric characteristic, a running characteristic, a power flow characteristic and the like, of a power grid, and is not completely suitable for safety and stability analysis and control of the power grid. Based on the accident chain model, existing two and three-defense configuration situations are considered, key element protection control action assessment indexes are proposed for quantizing uncertain factors of key element protection control, calculating an action probability of the key element protection control under a critical condition and determining subsequent events of a cascading failure accident chain; and in addition, according to the action probability of the protection control and the control cost required after an action, the risk of the accident chain is assessed, the high-risk cascading failure accident chain is screened, and an analysis basis is provided for preventing blackout due to cascading failure.