Single crystalline samples of type-Ⅷ Ba8Ga16-xGexSn30 (0 ≤ x ≤ 1.0) clathrates are fabricated by the Sn flux method. The structures and thermoelectric properties of the samples at temperatures ranging from 300 to 600 K are studied. Research results show that the actual content of Ge is relatively small in single crystal. The lattice parameters of the samples decrease slightly with the increase of the doping composition of Ge. The Ge doped samples have lower carrier density and higher carrier mobility than undoped samples. The Seebeck coefficients of all the doped samples are negative, and their absolute values are smaller than those of the undoped one. However, the electrical conductivity of the sample is increased by 62% after doping Ge and the sample of x=0.5 obtains a maximum value of ZT (1.25) at about 500 K.