A quasi-zero stiffness composite beam structure for controlling low-frequency vibration of a longitudinal axial flow threshing drum. The structure comprises a left column (2), a right column (3), a quasi-zero stiffness composite beam (5), a composite beam right connecting member (8), and a composite beam left connecting member (9). A right side of the quasi-zero stiffness composite beam (5) is connected to the composite beam right connecting member (8). A left side of the composite beam (5) is connected to the composite beam left connecting member (9). The composite beam right connecting member (8) is connected to the right column (3). The composite beam left connecting member (9) is connected to the left column (2). The composite beam right connecting member (8) and the composite beam left connecting member (9) are connected, at a quasi-zero stiffness composite beam bearing position, to a threshing drum shaft (603) via a threshing drum bearing seat (602). When the combined total stiffness of the positive sti
