Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio D_d/D_c and thickness ratio t_d/D_c is studied by a 3D(three-dimensional) numerical model developed in this paper, and compared with the results obtained through 2D(two-dimensional) numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method.Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns: ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio D_d/D_c and thickness ratio t_d/D_c are discussed in detail. Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio D_d / D_c and studied by a 3D (three-dimensional) numerical model developed in this paper, and compared with the results obtained through 2D (two-dimensional) numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyzes of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns: ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of along the radial direction is smaller than that of along the radial edge is the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio D_d / D_c and the thickness ratio t_d / D_c are discussed in detail.