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Digenite (Cu_1.8S) as a potential p-type thermoelectric (TE) material has attracted extensive attention due to its environmental benign, abundant resources and low cost of component elements. In this study, the TE properties of Cu_1.8S-x wt%BaTiO₃ bulk samples prepared by mechanical alloying (MA) combined with spark plasma sintering (SPS) were investigated. Adding BaTiO₃ would refine grains, thereby increasing the phonons scattering and reducing the thermal conductivity k. The k for Cu_1.8S-0.2 wt%BaTiO₃ is 2.2 W m^_-1 K^_-1 which is 18% lower than that for pristine Cu_1.8S (2.69 W m^_-1 K^_-1). The refined grains also enhance the carriers scattering, and reduce the carrier mobility to reduce the power factor (PF). Combine with the decreased PF and k, the calculated ZT values are barely unchanged for adding BaTiO₃ in Cu_1.8S. The Vickers-hardness for BaTiO₃-adding samples are improved due to the refined grains and the pinning effect of BaTiO₃ on grain boundary. This study shows that the mechanical properties of Cu_1.8S bulk samples can be effectively improved by compositing nano BaTiO₃ with little affecting TE properties, which provides ideas for preparing high mechanical properties and durable TE devices of Cu-S system.