The invention provides a rapid assessment method aiming at a thermal stability limit of a power grid section. The method comprises the following steps: (1) calculating an initial trend of a power grid, (2) performing N-1 breaking fault simulation, (3) determining whether various lines of the section runs at the thermal stability limit, and going to a step (4) or (9) according to judgment results, (4) generating a section branch active trend change rate matrix lambda, (5) generating a section active trend matrix P of the section running at a thermal stability limit state, (6) assessing the thermal stability limit of the section according to the active trend matrix P, (7) adjusting a power grid running mode according to an assessment result, (8) simulating the running mode after adjustment, and going to the step (4) or (9) according to the judgment result, and (9) outputting an assessment result of the thermal stability limit of the section. Through the assessment method, rapid assessment of the thermal stability limit of the power grid section can be achieved, a type of the fault is accurately positioned and limited, a set of the reliable thermal stability limit assessment method and a set of reliable thermal stability limit assessment flow are provided for power grid dispatching personnel, and a related theoretical basis is provided for software developers.