Abstract: In this paper, high melting point Half-Heusler alloy TaCoSb has been successfully prepared by powder sintering, high energy ball milling and DC rapid hot press process. The thermoelectric properties show that TaCoSb is a n-type thermoelectric material and σ= 0.58×10⁵ S·m^-1, κ= 3.8 W·m^-1 K^-1, S = -110 μV·K^-1, ZT=0.18 in 973K, respectively. This paper also researches the effect of Sn doping in Sb site on the thermoelectric properties of TaCoSb. We find that Sn doping has reduced the thermal conductivity and electrical conductivity of the material, the Seebeck coefficient slightly increases and the power factor decreases. Finally, the value of ZT doesn't significantly increase. Because of the low room temperature conductivity of TaCoSb, we should select the doping element in the Sb right side.