Abstract: Layered cobalt salts Bi₂Sr₂Co₂O_y display excellent thermoelectric performance.It is reported that changing degree of mismatch between layers can improve the electrical conductivity of materials, reduce the thermal conductivity and optimize the thermoelectric performance of materials.The polycrystalline Bi₂Sr_2-xM_xCo₂O_y (M=Ca, Ba; x=0, 0.05, 0.1, 0.15, 0.2, 0.25) thermoelectric bulk samples were prepared based on the classical solid-state reaction method in this paper.The samples' crystal phase, structure and morphology were characterized and analyzed by using XRD and SEM.The results showed that when Ba and Ca go into lattice and occupy the Sr site, With the increase of Ba and Ca doping amount, the total thermal conductivity and resistivity are remarkably decreasedand the materials of ZT value significantly increased.When doping amount x = 0.2, ZT of the Bi₂Sr_1.8Ba_0.2Co₂O_y and Bi₂Sr_1.8Ca_0.2Co₂O_y sample gets to its maximum and reaches 0.22 and 0.41 at 973 K respectively.This results in significant improvement in thermoelectric performance.