The embodiment of the invention discloses a power failure diagnosis method. The method comprises the following steps of: receiving an input power failure equipment node; according to the power failure equipment node, in a power grid topology model, acquiring power equipment nodes directly connected with the power failure equipment node; judging whether at least one of the acquired power equipment nodes is located in a power cut range, if so, diagnosing the power failure as a power-cut affected power failure; otherwise, diagnosing the power failure as an unknown failure, wherein the power cut range refers to a power grid topology containing preset power-cut power equipment nodes and nodes below the power-cut power equipment nodes in the power grid topology model. The embodiment of the invention also discloses a power failure diagnosis device. When the method and device disclosed by the embodiment of the invention are adopted for diagnosing power failures, the diagnosis efficiency can be increased, and the diagnosis effect can be improved.