Abstract: Submicron tungsten-osmium mixed powders with the different content of Os (atomic number fraction) were prepared by solid‒liquid mixing method. The tungsten-osmium mixed matrix disperser cathodes with the uniform pore structure were obtained by microwave sintering. The electron emission testing results show that, the addition of Os obviously improves the emission performance of the impregnated tungsten-based dispenser cathode. The W–25Os cathode (Os atomic number fraction is 25%) exhibits the relatively low work function and high emission current density. At 1100 ℃, the pulse emission current density of the W–25Os cathode is 42.86 A·cm⁻² with the emission slope of 1.40, which is 1.7 times of the conventional barium-tungsten dispenser cathodes under the same working conditions and up to the electron emission level of M-type cathodes. The W–25Os cathode shows the low effective work function as 1.93 eV, which is conducive to the generation of active free barium source. The molar ratio of surface elements Ba:(W+Os) is 0.83:1.00, which is significantly higher than that of the traditional barium tungsten cathode (about 0.50:1.00).