•The convection in the micro THs center declines with the increasing ARs from 6.25:1 to 1.67:1.•The convection-dependent additives formed diverse adsorption states with different convection.•The defect-free filling process gradually converted into the insufficient filling process with decreasing ARs.•The micro THs with AR above 3.33:1 can be fully filled with a uniform bright Cu surface preferentially orientated to (111). In this work, we combined the computational simulation and experiments to explore the convection on filling characteristics of the micro through-holes (THs) with multiple aspect ratio (ARs). The micro THs with ARs 6.25:1∼1.67:1 (thickness 500 μm) were chosen as research targets. The computational model was established based on the actual state of Haring-Cell, and attention was fixed on the convection distribution in the micro THs. The interaction mechanism of additives with the changing ARs systematically explored by electrochemical measurements. The simulation results show that the convection in the micro THs center declines with the increasing AR. The convection-dependent additives formed diverse adsorption states around the micro THs with different ARs, providing two kinds of Cu filling processes, including defect-free filling and insufficient filling. The weak convection is conducive to the adsorption of the accelerator and detrimental to the adsorption of the suppressor, which accelerates the Cu electrodeposition and elevates the throwing power (TP) value to over 100% to form the defect-free filling. Strong convection is instrumental in the adsorption of the leveler so that a uniform Cu film thickness can be obtained but to create the insufficient filling. Simulation and electroplating experiments show that the AR of 3.33:1 is the cut-off point of the flow field distribution and the electroplating processes. The micro THs with AR higher than 3.33:1 can be fully filled with a uniform bright Cu surface.