Transcranial Magnetic Stimulation (TMS) is a non-invasive neuromodulation technique that has been extensively applied in both clinical therapy and neuroscience research. The performance of TMS largely depends on the geometry of the stimulation coil, which determines the spatial distribution and focality of the induced intracranial electromagnetic fields. To enhance focality without compromising stimulation intensity, this study proposes a three-layer gradient excitation coil derived from the conventional Figure-of-Eight (FOE) configuration. The design integrates a multi-stage circumferential shielding structure with graded properties, which effectively suppresses eddy currents and reduces field leakage. This non-uniform shielding approach enables better control over the spatial confinement of the induced electric field, further improving stimulation precision.Finite element simulations were conducted to evaluate the stimulation characteristics and analyze the synergistic influence of structural parameters. The results demonstrate that the proposed coil achieves simultaneous enhancement of both stimulation intensity and focality compared with the conventional FOE coil. Moreover, the inclusion of the optimized shielding structure further minimizes off-target activation and enhances energy utilization efficiency. Overall, this work provides an effective strategy for improving the precision of TMS-based neuromodulation while reducing unintended stimulation.