Abstract: Mg₃（Sb, Bi）₂-based thermoelectric materials attract a lot of attention because of their high performance,environmental protection and economy, but their thermoelectric properties still need to be improved in practical applications.The electric transport performance and thermoelectric transport performance are optimized by adjusting the grain size. The results show that through the regulation of carrier concentration and the suppression of grain boundary scattering, the power factor of Mg_3.22Ho_0.03Sb_1.5Bi_0.5material is as high as 19.38 μW·c^-1·K^-2at 600 K and the average power factor is about 17.4μW·c^-1·K^-2when the sintering temperature is chosen to be 1073 K. On the other hand, the point defects caused by doping contribute to the reduction of lattice thermal conductivity would also be helpful. At 750 K, these point defects reduce the lattice thermal conductivity to 0.47 W·m^-1·K^-1. The combined electrical and thermal properties are tuned up to a ZT value of1.7 for Mg_3.22Ho_0.03Sb_1.5Bi_0.5.