A novel structural composite yarn was fabricated by periodically forcing filaments with harmonic migrations toenhance the cooperativity between filaments and staple fibers. The geometrical principle of yarn structure variations causedby harmonic migrations of filaments was theoretically analyzed, then demonstrated the influences of filament’s positions ondifferent shapes of the composite spinning-triangle zone. Further, the novel structural composite yarn structure was comparedto the seven models of composite yarns which were established with different filament’s positions, showing a varied filamenthelical structure to capture and then lock internal and external staple fibers, distinguishing that other composite yarns inliterature. Then, a synergetic eccentric device was employed to oscillate two filaments to conduct confirmatory tests. Theonline observations of the dynamic spinning-triangle zone were technically applied to evaluate the filaments’ harmonicmigrations. Furthermore, the yarn structural variations were caused by various geometrical configurations. Experimentalresults exhibited that the novel structural composite yarn had relatively fewer hairiness, medium irregularity, and strengthafter comparisons with other composite yarns. Altogether, the cyclically harmonic migrations of filaments were promising asan efficient and novel method for control the configurations between filaments and staple fibers.