The invention provides an online fast local topology analysis method suitable for a large power grid. The online fast local topology analysis method comprises the following steps: establishing a local topology analysis data model, and defining a data structure; determining a basic bus analysis range and a local bus analysis range; carrying out topology analysis for the basic bus analysis range; carrying out topology analysis for the local bus analysis range; and analyzing local system topology based on local bus topology analysis algorithm and result. The method is high in practicability, and can be used for solving the problem of quickly analyzing and calculating the topology of the large power grid under a remote signaling deflection condition of the power grid, tracking and updating the topology result in real time, flexibly defining the local topology analysis range, realizing fast topology analysis of the power grid within a self-defined range, providing a calculation and analysis foundation for scheduling various high level applications in an automatic system and further improving the practicability of an online analysis application.