As a type of medium-temperature thermoelectric materials, Mg₂(Si,Sn) alloy thermoelectric materials have been widely concerned because of the low cost and environmental friendliness. Heavily Sb doping can effectively induce Mg vacancy so as to reduce the thermal conductivity in Mg₂(Si,Sn)-based materials, but at the same time lead to a decrease of Seebeck coefficient. In this study, high-quality Mg_2.12-ySi_0.4Sn_0.5Sb_0.1Zn_y (y=0-0.025) samples were successfully synthesized by high temperature melting and vacuum hot-pressing method. Zn element was introduced into the heavily Sb-doped Mg₂(Si,Sn) material to investigate the double doping effect on the electroacoustic transport properties. The results show that Zn-Sb double doping could effectively reduce the total thermal conductivity of Mg₂(Si,Sn)-based materials by obviously suppressing the electronic thermal conductivity and at the same time enhance the Seebeck coefficient of Zn-doped samples, so as to compensate for the loss of electrical conductivity, and maintain high electrical performance. Significantly optimized thermal conductivity and electrical performance ultimately improve the thermoelectric figure of meritZT of the material. At 823 K, the maximum ZT of Mg_2.095Si_0.4Sn_0.5Sb_0.1Zn_0.025 reached 1.42.