Combining thermoelectric materials with magnetocaloric materials enables a potential new all-solid-state cooling technology based on coupling enhancement of thermoelectric cooling and magnetic cooling, which is highly expected to achieve a technological change from thermoelectric cooling to thermoelectromagnetic cooling. However, the stability of thermal-electro-magnetic composites in service environment is still unknown. Herein, a series of Gd/BST thermo-electro-magnetic gradient composites were prepared by combining Bi_0.5Sb_1.5Te₃ (BST) thermoelectric material and Gd magnetocaloric material via spark plasma sintering technology. Evolution of phase composition, microstructure, thermoelectric, and cooling performance of the gradient composites during the 12 d aging process at 338 K and 80% relative humidity(RH) were systematically studied. The results show that the phase composition and microstructure of Gd/BST thermal-electro-magnetic gradient composites have excellent service stability. The chemical composition and average thickness (~4.5 μm) of Gd-Te diffusion layer at Gd/BST heterogeneous interface doesn’t exhibit obvious change during the aging process. The test of thermoelectric and cooling performance along different Gd concentration gradient indicates that ZT of the materials negligibly changed before and after aging treatment, and the cooling temperature difference of the single-leg device is stable at about 6.5 K under the threshold current of 2.5 A. These results show that thermoelectric and cooling performance of the Gd/BST gradient composites have excellent service stability.