In order to obtain LaB6 cathode with high-purity and excellent properties，La and LaH2 nanopowders were prepared by hydrogen arc plasma method, and then La-LaH2 and B nanopowders were sintered to fabricate the high-purity LaB6 polycrystal nano-bulk cathode by in situ SPS (Spark Plasma Sintering) in a oxygen free system. The effects of sintering temperature and pressure on the phases, microstructure and properties of the nano-bulk were systematically studied. The results show that the single-phase LaB6 was formed in the nano bulk with a high purity of 99.867％ and an average crystal size of about 120 nm. The relative densities of nano-bulk LaB6 is up to 99.2%, and its hardness is up to 17.4 GPa, the bend strength of the polycrystal LaB6 is as high as around 245.6 MPa, the theoretical bend strength value of single crystal