The single-phase p-type Ag0.5(Pb8-xSnx)In0.5Te10 compounds were prepared by melt reaction and spark plasma sintering (SPS). Influences of Sn substitution for Pb on the carrier transport property and thermoelectric properties of the Ag0.5(Pb8-xSnx)In0.5Te10 (x=2, 2.5, 3, 3.5, 4) were investigated. Results indicate that: the carrier concentration and electrical conductivity increase with the increase of Sn substitution fraction x, the carrier mobility remains stable with the increase of x, the Seebeck coefficient and lattice thermal conductivity decrease with the increasing of x. Thermal conductivity decreases further after spark plasma sintering. The dimensionless figure of merit ZT of Ag0.5(Pb5Sn3)In0.5Te10(after SPS) reached a high maximum value of 1.05 at 700K.