Abstract: The structure and characteristic of an electron gun with a plasma spray LaB_6cathode for medical electron linear accelerator are described in the paper. Theemission, poison and stability performances of scandium salt Ba-W, plasma sprayLaB_6, polycrystalline LaB_6 and pure Ta cathodes are measured. The results showthat the plasma spray LaB_6 cathode is more suitable for the medical electron linearaccelerator with detachable vacuum system than others.