The invention belongs to the technical field of nuclear power maintenance, and particularly relates to a nuclear power plant pre-maintenance project overdue early warning method and device. The invention provides an overdue early warning method for a pre-maintenance project of a nuclear power plant. The method comprises the following steps: judging a relationship between an executed condition of afirst project and a plurality of preset conditions; under the condition that the executed condition of the first project is matched with one of a plurality of preset conditions, determining an expiration degree corresponding to the first project according to an expiration determination mode corresponding to the matched preset condition; judging whether the determined overdue degree is matched with a preset overdue condition or not; and performing overdue reminding under the condition that the overdue degree is matched with a preset overdue condition. According to the embodiment of the invention, the conditions of unexpected pre-maintenance overdue, periodic test overdue and the like caused by the problems of inaccurate deadline calculation, non-uniform rules and the like are reduced, theunified management of each power plant is facilitated, and the safe and stable operation of the nuclear power plant is facilitated.