This letter presents an eccentric inverted-cone three-dimensional transcranial magnetic stimulation (TMS) coil to address the poor focusing ability and small effective stimulation depth in commercial TMS coils. The performance of the coil is compared with that of several commercial and theoretical coils via finite element modeling. Spherical head model simulations reveal that the coil outperforms existing coils in terms of focusing ability and effective stimulation depth. Furthermore, employing a dual-coil combination effectively enhances the maximum induced electric field strength and increases the focusing ability and effective stimulation depth of the signal.