As an important high-temperature thermoelectric materials, SiGe alloy has been concerned and used widely. Although the dimensionless thermoelectric merit (ZT) of n-type SiGe alloys thermoelectric material has made much great progress, the ZT of p-type SiGe alloys is still low. In this paper, p-type Si80Ge20Bx (x = 0.5, 1.0, 2.0) alloys thermoelectric materials were prepared by one-step alloying method using Si, Ge and B powders as raw materials. The composition, microstructure and thermoelectric properties of the samples were characterized and analyzed. The results show that, in-situ one-step alloying followed by spark plasma sintering can be realized and bulk materials can be obtained. With the increase of B doping content, the electrical conductivity increases significantly and the thermal conductivity decreases significantly. When the temperature is 950 K, the thermal conductivity is 1.79 W/(m K). At 1050 K, ZT reaches the maximum value of 0.899. Due to the synergistic effect of ball milling and doping, different types of defects are produced in SiGe structure matrix resulted in scattering of different wavelengths of phonons, leading to the decrease of thermal conductivity of SiGe alloy.