Considering the reliable operation of Gas – Insulated Switchgear (GIS) system within higher voltages, the optimal performance of solid spacer is one of the most effective topologies in improving the quality of this system. The quality of GIS system is related to the minimization of maximum electric field strengths at hot triple junctions along the tracing paths defining the geometrical zone of field intensification considering spacer material, insu- lation material and electrodes. In this research, the operational features of the proposed Basin Cone – Shaped Spacer (BCSS) is enhanced considering the optimum design of spacer material utilizing the technology of Functionally Graded Material (FGM). For first methodology step, the Gaussian Distribution Function (GDF) technology is innovatively provided to normally distribute the FGM permittivity along the proposed BCSS model. To overcome the randomness of GDF in normalizing efficiently the weighed data, the proposed optimizers of Water Cycle Algorithm (WCA), Moth – Flame Optimization (MFO) and Fire Hawk Optimizer (FHO) are provided to optimize GDF coefficients for optimal distribution of FGM permittivity. Then, the stability of the proposed optimizers is studied to efficiently validate the effectiveness of their estimated results. In next step, this paper provides an innovative methodology to calculate the optimum number of layers of the proposed BCSS model with FGM technology regarding the industrial constraints and the proposed optimizers. Then, the optimal permittivity distribution scenarios with the optimum GDF coefficients and number of BCSS layers are defined for the field strength calculation along the proposed tracing paths containing the intensified triple junctions using COMSOL Multiphysics 6.0 program with the computation of Finite Element Method (FEM). Comparatively, the compu- tational efficiency of field strengths of the optimal FGM permittivity distribution scenarios is validated consid- ering the common distributions without FGM and the standard distributions of this technology