Leveler is essential in the electroplating process of the through-hole (TH), the adsorption characteristics of which are strongly influenced by the aspect ratios of the THs. However, only a single kind of leveler usually appears in the most frequently performed THs’ filling electrolyte, which is highly possible to limit the electrolyte's capability to fill THs and improve the copper film properties. In this paper, two levelers, 2-Thiazoline-2-Thiol (T1) and Nitrotetrazolium Blue chloride (NBT), with significant molecular weight differences, were combined to fill THs with multiple ARs. The interactions among the leveler compounds and other additives become the primary factor controlling the THs electroplating process, which was systematically investigated through a combination of flow field numerical simulation and electrochemical measurements. T1 presents a weaker inhibition effect and is more sensitive to convection than NBT, which also exhibits a convection-enhanced inhibition effect with other additives. The convection of the electrolyte in the THs center continuously decreases with the ARs, guiding to the increasing electroplating rate at the THs center, high throwing power (TP) of 141%, and flawless filling of the THs with ARs of 4.75:1∼1.9:1 in 2.5 h. The copper film on the surface maintains extremely high flatness and low thickness.