The complex coupling between thermoelectric parameters makes it extremely challenging to improve the performance of materials. Typically, the reduction of thermal conductivity by incorporating porous structures often leads to a compromise in electrical conductivity. Herein, we present high-ion-conductive zeolite X (including Na-, Ca-, and Li-low silica type-X (LSX)) as the subnanoporous additive in the Bi_0.4Sb_1.6Te₃ (BST) matrix. Owing to the high pore charge density of zeolite X, the decrease in conductivity is effectively suppressed while maintaining a low thermal conductivity. Positively charged metal cation (M⁺) and valence electron of oxygen atom in aluminum-oxide tetrahedron of zeolite X achieve charge balance. Cationic with different electronegativity regulated electrons of oxygen atom transferred from the oxygen atoms to the BST matrix. The lower electronegativity of Na⁺ leads to a higher electron density surrounding oxygen atoms in Na-LSX. Thus, more electrons are transferred to the BST matrix from the oxygen atoms in Na-LSX and form Te–O bonds. Ultimately, the figure-of-merit (ZT) peak of BST/0.8 wt.% Na-LSX nanocomposites reached 1.47 at 373 K, with a huge cooling temperature difference of 69.4 K and an excellent thermoelectric conversion efficiency of 6.95%. This work exploits the stable and unique three-dimensional pore structure of X-type molecular sieves, broadening their potential application in the thermoelectric medium temperature range.