The invention relates to an overall-modal extraction method. The overall-modal extraction method includes 1, establishing a beam element model of an overall structure, 2, reading node information and modal order of an overall finite element model and acquiring inherent frequency of modal at different order of the overall finite element model and feature vector related to mass matrix normalization, 3, extracting nodes according to node information, selecting the extracted nodes as major nodes of core pole and assistors, and nodes corresponding to branches of engines and effective load branches, 4, appointing normalized node number, 5, judging main vibration direction, 6, acquiring feature vector and generalized mass normalized according to appointed nodes, and 7, outputting modal results. With the overall-modal extraction method, efficiency of modal extraction is greatly improved and risks caused by failure from manual modal extraction are reduced.