The invention discloses a fast calculation method for capacity optimal matching based on a grouping capacity coding method. When a power system breaks down and is controlled emergently, after the capacity of a generator to be cut off is calculated, and selection is conducted on generators allowed to be cut off. In order to achieve the optimal control effect, it is required that the matching error of the capacity of the generator to be removed and the capacity to be cut is the minimum, when the number of the generators is large, the calculated quantity is much large, in order to fast find the optimal match, the generators are divided into two or more groups, a weighing offset address with the weight is distributed to each generator in each group first, then address coding is conducted on each arrangement combination of the generators in each group, the corresponding capacity code of each address code is calculated, and the optimal matching capacity can be calculated out rapidly by scanning the mutual intersection points of each group of codes. If the address codes of each group are mapped to a coordinate axis in a coordinate system, a searched object is mapped into an intersection point in a coordinate plane, and the searched object is shown in the drawing in the abstract.