A series of Ba8Ga15XSi30(X=Ga、Zn、Cu) clathrate samples were prepared by combining arc melting, ball milling and spark plasma sintering(SPS) techniques. The crystal structure and thermoelectric properties of all samples were studied. Compared with Ba8Ga16Si30, the lattice constant a decreases as one Ga is replaced by Zn or Cu. What's more, thermal conductivity decreases and magnitude of Seebeck coefficient increases with Zn or Cu doping. Consequently, thermoelectric figure of merit ZT increases significantly...