In this paper, rhenium-tungsten core-shell powder was prepared by solid-liquid mixing method and then osmium powder was added to prepare ternary mixed powder with special coating structure after pretreatment. After the powder was pressed, sintered, impregnated with salt, washed and annealed, a ternary mixed-base cathode of tungsten-rhenium osmium was prepared. After impregnation with 411 salt, the pulse emission test found that W2Re1Os1 cathode which is a ternary mixed-base cathode has the best electron emission performance and the current emission density can reach 35 A/cm² at 1050℃, which is slightly higher than that of the same type of binary mixed-base cathode, reaching the level of the ternary film cathode covered with tungsten, rhenium and osmium. It is verified by experiments that neither Re nor Os reacts with the active salt during the impregnation process of the ternary tungsten-rhenium-osmium mixed-base cathode, and the active substance is produced by the reaction of W and the active salt.